PRIORITY DOCUMENT

[0001] The present application claims priority from Australian Provisional Patent Application No. 2021901100 tided “APPARATUS AND PROCESS FOR SOLAR EVAPORATION-BASED SOIL REMEDIATION” and filed on 14 April 2021, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates generally to soil remediation and more specifically to apparatus and processes for solar evaporation-based soil remediation.

BACKGROUND

[0003] Pollution of soil caused by heavy industries including metal mining, smelting and untreated wastewater is harmful for the growth of plants. Plants will take up contaminants, which, in turn, pass through the food chain and ultimately pose a risk to human health. Common contaminants in soils include heavy metals such as copper (Cu), cadmium (Cd), chromium (Cr), zinc (Zn), lead (Pb) and mercury (Hg), arsenic (As), organic dyes such as Rhodamine B (RhB), methyl orange (MO), methyl blue (MB), and pesticides such as insecticides and herbicides. Soil salination is also a long lasting concern, because it impacts agriculture productivity, reduces plant diversity and causes loss in surface vegetation.

[0004] Current technologies for soil remediation can be divided into three major categories: biological treatment, chemical treatment, and physical treatment (see, for example, Yanyan Gong, el al. Water Research, Volume 147, 15 December 2018, pages 440-460). Examples of biological treatment technologies include bioventing and phytoremediation. Examples of chemical treatment technologies include solidification/stabilization, precipitation and ion exchange. Examples of physical treatment technologies include soil replacement, vitrification, electrokinetic separation and encapsulation.

[0005] Among the various remediation technologies, phytoremediation is a potential solution for eco- friendly remediation of contaminated soil. Phytoremediation is a process that uses plants to remove, transfer, stabilise, and destroy contaminants in soil. The mechanisms of phytoremediation include enhanced rhizosphere biodegradation, phyto-extraction (also called phyto-accumulation), phytodegradation, and phyto-stabilization. Phyto-stabilization makes use of plants to produce chemical compounds and thereby immobilise contaminants at the interface of roots and soil. [0006] Unfortunately, phytoremediation is an inefficient process, has low remediation capacity and is limited by soil and environmental conditions. To this end, biomimicry of evaporative hydrostatic pressure and capillarity in vascular plants has been proposed by Mathew J.B. Swallow, el al. ( Science of The Total Environment , Volume 655, 10 March 2019, Pages 84-91) as a means of saline soil remediation, which uses evapotranspiration to translocate saline soil water above the soil surface where it is effloresced with ferrocyanides. Zhi Zhao el al. developed a method to synthesise a hyper-branched biomimetic hydrogel network across a soil matrix to improve the mechanical strength of the loose soil and simultaneously mitigate potential contamination due to excessive ammonium {Environ. Sci. Technol. 2016, 50, 22, 12401-12410), wherein the hydrogel network possesses the water retention, ion absorption, and soil aggregation capabilities of plant root systems in a chemically controllable manner. However, an improvement in remediation efficiency is desirable.

[0007] Accordingly, there is a need for an eco-friendly in-situ soil remediation devices and methods that have satisfactory performance in one or more of the following aspects: (i) facilitates sampling of an aqueous fluid from a contaminated soil; (ii) improves remediation efficiency; (iii) achieves long-term continuous remediation; and (iv) is cost effective. Alternatively, or in addition, there is a need for soil remediation devices and methods that provide an alternative to existing soil remediation devices and methods.

SUMMARY

[0008] In a first aspect, provided herein is a solar driven in-situ soil remediation apparatus comprising: at least one fluid capillary channel configured to draw in and transport an aqueous fluid from a contaminated soil by capillary action when in contact with the contaminated soil; and a solar absorber comprising a photothermal material loaded on a porous material, the solar absorber in fluid connection with the at least one fluid capillary channel and configured to generate heat under solar irradiation so as to accelerate evaporation of the aqueous fluid from the apparatus, wherein at least some of any contaminants from the contaminated soil that are drawn into the apparatus in the aqueous fluid are retained in the apparatus.

[0009] In certain embodiments of the first aspect, the apparatus further comprises a water collector in fluid connection with the solar absorber, the water collector being configured to condense evaporated water from the aqueous fluid into liquid water and return the latter to the soil.

[00010] In a second aspect, provided herein is a solar driven in-situ process for soil remediation, said process comprising: contacting at least one fluid capillary channel with a contaminated soil to draw in and transport an aqueous fluid from the soil by capillary action; and exposing a solar absorber comprising a photothermal material loaded on an porous material and in fluid connection with the at least one fluid capillary channel to solar irradiation to generate heat so that evaporation of the aqueous fluid is accelerated and contaminants from the soil are retained by the at least one fluid capillary channel and/or the solar absorber.

[00011] In certain embodiments of the second aspect, the process further comprises condensing evaporated water from the aqueous fluid into liquid water and returning the latter to the soil through a water collector in fluid connection with the solar absorber.

[00012] In certain embodiments of the first and second aspects, the contaminants to be removed from the soil are selected from one or more of heavy metal ions, organic pollutants, endocrine disrupting chemicals (EDC), and particulate matter. In certain specific embodiments, the heavy metal ions are selected from As ³⁺ , Pb ²⁺ , Cu ²⁺ , Cd ²⁺ , Cr ³⁺ , Zn ²⁺ and Hg ²⁺ . In certain specific embodiments, the organic pollutants are selected from coomassie brilliant blue, rhodamine B, congo red, methylene blue, Aldrin, Atrazine, Chlordane, Chlorpyrifos, Chlordecone, Decabromodiphenyl ether, Dicofol, DDT, Dieldrin, 2,4- D, Endrin, Glyphosate, Heptachlor, hexachlorobenzene (HCB), hexabromobiphenyl, hexabromodiphenyl ether, heptabromodiphenyl ether, alpha hexachlorocyclohexane, beta hexachlorocyclohexane, hexabromocyclododecane, hexachlorobutadiene, Lindane, Mirax, Toxaphene, pentachlorobenzene, pentachlorophenol, polychlorinated biphenyls (PCB), polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated naphthalenes, short-chain chlorinated paraffins, tetrabromodiphenyl ether, pentabromodiphenyl ether, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and polychlorinated dibenzofurans (PCDF). In certain specific embodiments, the endocrine disrupting chemicals are selected from lead, phthalates, cadmium, dioxins, bisphenol A (BPA), phthalates, phenol, brominated flame retardants, polychlorinated biphenyls (PCBs), parabeans, UV filters, Triclosan, and perfluorochemicals. In certain specific embodiments, the particulate matter is microplastics. For example, the solar driven in-situ remediation apparatus of the disclosure is used to remove Pb ²⁺ , PFOS, and/or PFOA.

[00013] In certain embodiments of the first and second aspects, the apparatus comprises a plurality of fluid capillary channels. The plurality of fluid capillary channels may be provided by a porous sponge. As used herein, the term "sponge” means a porous material having open cells and/or interconnected cells. In some embodiments, the sponge can be formed from any suitable hydrophilic porous material such as melamine sponge, cellulose sponge, carbon sponge, cotton rod, cloth roll or porous hydrogels. In other embodiments, the sponge can be formed from porous hydrophobic materials coated with a hydrophilic surface layer, e.g. porous polyurethane coated with a hydrophilic polydopamine layer. In some further embodiments, the sponge can be a natural sponge, such as honeycomb natural sponge. [00014] In certain embodiments of the first and second aspects, the porous sponge comprises an adsorbent material having an affinity for one or more contaminants present in the soil. The porous sponge may be formed from the adsorbent material or the porous sponge may be a non-active sponge support material having an adsorbent material coating. The non-active sponge support material may be any one or more of those sponges outlined above. The adsorbent material used herein is selected from, but not limited to, polyelectrolyte complex (PEC), sodium alginate and hydroxyapatite. In some specific embodiments, the adsorbent material is a polyelectrolyte complex (PEC). The PEC may be selected from PDopa-PAH PEC and chito san-based PEC. For example, the PEC sponge is a PDopa-PAH PEC prepared from poly (ally lamine hydrochloride) (PAH) and poly (L-3,4-dihydroxyphenylalanine) (PDopa), which is optimised for application. PECs may be particularly suitable for adsorbing or binding to heavy metal ions present in the soil. In other specific embodiments, the adsorbent material is sodium alginate. The nontoxicity and high biodegradability of sodium alginate could make the adsorbent material environmentally friendly. In certain embodiments, the porous sponge has an average pore size ranged between tens of nanometers and hundreds of micrometers. In certain embodiments, the porous sponge has a porosity of about 50 to 95%.

[00015] In certain embodiments of the first and second aspects, the porous sponge used to form the fluid capillary channels is also used for the porous material comprised by the solar absorber. Thus, in certain embodiments the solar absorber comprises a porous sponge as the porous material. The porous sponge comprises an adsorbent material having an affinity for one or more contaminants present in the soil. The porous sponge may be formed from the adsorbent material or the porous sponge may be a non-active sponge support material having an adsorbent material coating. The non-active sponge support material may be those sponges outlined above. The adsorbent material used herein is selected from, but not limited to, a polyelectrolyte complex (PEC), sodium alginate and hydroxyapatite. The PEC may be selected from PDopa-PAH PEC and chitosan-based PEC. For example, the PEC sponge is a PDopa-PAH PEC prepared from poly(allylamine hydrochloride) (PAH) and poly (L-3,4-dihydroxyphenylalanine) (PDopa), which is optimised for application. In certain embodiments, the porous sponge has an average pore size ranged between tens of nanometers and hundreds of micrometers. In certain embodiments, the porous sponge has a porosity of about 50 to 95%.

[00016] In certain embodiments of the first and second aspects, a melamine sponge with a PDopa-PAH PEC coating is used as the porous sponge. In certain embodiments, reduced graphene oxide (RGO) is used as the photothermal material and is coated onto the porous sponge to form the solar absorber.

[00017] In certain embodiments of the first and second aspects, the photothermal material is selected from, but not limited to, graphene oxide (GO), reduced graphene oxide (RGO), graphite, carbon nanotubes (CNT), polypyrrole (PPy), carbon black nanoparticles, biomass carbon, polydopamine, black nickel, CuO, Cu _2-x S (0<x<2), Fe ₃ 0 ₄ , Co ₃ 0 ₄ , Ti ₂ 0 ₃ , TiN, CuFeS ₂ , and plasmonic metal (e.g. Au). BRIEF DESCRIPTION OF THE FIGURES

[00018] Non-limiting embodiments of the present disclosure will be discussed with reference to the accompanying figures wherein:

[00019] Figure 1 shows a schematic representation of the biomimetic structure of the present apparatus in terms of tree structure.

[00020] Figure 2 shows an experimental representation of the solar driven biomimetic in-situ soil remediation apparatus according to an embodiment of the disclosure.

[00021] Figure 3 shows open cells contained within PEC coated sponge.

[00022] Figure 4 shows a comparison of solar absorbance of sponge, PECs coated sponge and RGO- PECs coated sponge.

[00023] Figure 5 shows a schematic process for preparing RGO-PECs coated sponge.

[00024] Figure 6 shows evaporation performance of the solar driven biomimetic in-situ soil remediation apparatus according to embodiments of the disclosure.

[00025] Figure 7 shows long-term evaporation performance of an embodiment of the solar driven biomimetic in-situ soil remediation apparatus (a) A continuous water injection system (b) Evaporation tests (c) Evaporation rate during 2 weeks (d) Environmental Temperature and humidity change during evaporation test. (Grey areas represent night time irradiation).

[00026] Figure 8 shows contaminant reduction and remediation performance for each of a blank control, the phytoremediation, a solar driven biomimetic remediation according to the disclosure (a) A schematic phytoremediation and solar evaporation remediation systems (b) Concentrations of Pb ²⁺ under different extraction conditions (F1-F5 described herein) for a blank (left), a soil treated by phytoremediation using rye grass (centre), and a soil treated using a solar driven biomimetic in-situ soil remediation apparatus according to the present disclosure (right) (c) Adsorption in the roots (left) and shoots (right) of a phytoremediation system using rye grass and a solar driven biomimetic in-situ soil remediation apparatus according to the present disclosure (d) Adsorption in the roots (left) and shoots (right) of a phytoremediation system in a blank, using rye grass and a solar driven biomimetic in-situ soil remediation apparatus according to the present disclosure (e) Plants grown in a blank soil (left), in a soil treated by phytoremediation using rye grass (centre), and a soil treated using a solar driven biomimetic in-situ soil remediation apparatus according to the present disclosure (right). [00027] Figure 9 shows a schematic representation of a solar driven in-situ soil remediation apparatus with water recycling according to embodiments of the disclosure.

[00028] Figure 10 shows a schematic process for preparing rGO-SA sponge and its characterisation (a) The fabrication process of the SA sponge and rGO-SA sponge (b) Light adsorption spectra of the unmodified sponge, SA sponge and rGO-SA sponge (c) Water droplet contact angle test of top surface of rGO-SA sponge. SEM images of the initial sponge (d), SA sponge (e), and rGO-SA sponge (f,g).

[00029] Figure 11 shows a schematic process for preparing rGO@«HAP@Alg cellulose sponge and its characterisation (a) Synthesis process for rGO@«HAP@Alg cellulose sponge (b) SEM image of pristine cellulose sponge (c) SEM image of «HAPri Alg cellulose sponge (d) SEM image of «HAR on the surface of rGO@nHAP@Alg cellulose sponge (e) SEM image of rGO@«HAP@Alg cellulose sponge.

(f) Absorption of a water droplet on «HAPri Alg cellulose sponge surface (g) Capillary water rise test.

(h) Schematic diagram of the evaporator with different leaves number (i) Variation in heavy metal adsorption capacity with different heavy metals.

[00030] Figure 12 shows solar evaporation of soil water (a) Mass change (i.e., soil water) of the soil, unmodified sponge, SA sponge and rGO-SA sponge (b) Mass change with different soil water content under 1 sun illumination for rGO-SA sponge (c) Variation in evaporation rate with solar intensity and wind velocity for rGO-SA sponge (d) Average evaporation surface temperature of the rGO-SA sponge under 1 sun illumination (e) IR images of the evaporation surface under 1 sun illumination.

[00031] Figure 13 shows outdoor solar evaporation performance (a) The changes in temperature and solar flux in a typical 8 hour outdoor testing period (b) Soil water evaporation performance during the 8 hour period (c) The variation in evaporation rate during continual 12 days of outdoor evaporation test.

[00032] Figure 14 shows evaporation performance with rGO@«HAP@Alg cellulose sponges (a) Evaporation performance under dark and light illumination for a 2 cm height evaporator with 3 leaves (b) Variation in evaporation rate of the 3 leaves evaporator with different height under 1 sun illumination (c) Variation in evaporation rate of the 3 cm height evaporator with different leaf number (d) Temporal variation in the average temperature of the top layers of the leaf for the 24 leaves evaporator with 3 cm height under 1 sun illumination (e) IR images of evaporators having different leaf numbers for a 3 cm height evaporator after 30 minutes under 1 sun illumination.

[00033] Figure 15 shows changes in Pb concentration in rGO-SA sponge after indoor and outdoor solar evaporation, and (a) soluble Pb content in soil after indoor and outdoor solar evaporation (b).

[00034] Figure 16 shows heavy metal content in soil porewater before and after solar driven evaporation remediation (SDER). DESCRIPTION OF EMBODIMENTS

[00035] The disclosure arises from the inventors' research into the evaporation on plant leaves and solar driven photothermal effects that result therefrom. Evaporation on plant leaves can create a negative water vapor pressure, which, together with capillary action within the numerous cellulose-based channels of the plants, is considered to drive transport of water and other substances including minerals from soil through roots to shoots. It has been surprisingly found by the inventors that an improved remediation of contaminated soil can be achieved through a combination of fluid channels that mimic the numerous cellulose-based channels of plants and a photothermal material loaded upon a porous sponge that performs a similar function to transpiration of plants but is much faster. This is illustrated in Figure 1.

[00036] Disclosed herein is a solar driven biomimetic in-si tu remediation apparatus. The apparatus comprises at least one fluid capillary channel configured to draw in and transport an aqueous fluid from a contaminated soil by capillary action when in contact with the contaminated soil. The apparatus further comprises a solar absorber comprising a photothermal material loaded on a porous material. The solar absorber is in fluid connection with the at least one fluid capillary channel and configured to generate heat under solar irradiation to accelerate evaporation of the aqueous fluid from the apparatus. The targeted contaminants from the contaminated soil that are drawn into the apparatus in the aqueous fluid are retained in the apparatus by the adsorbent materials used herein.

[00037] Optionally, the apparatus further comprises a water collector in fluid connection with the solar absorber. The water collector is configured to condense evaporated water from the aqueous fluid into liquid water and return the latter to the soil.

[00038] Also disclosed herein is a solar driven in-situ process for soil remediation, said process comprising: (i) contacting at least one fluid capillary channel with a contaminated soil to draw in and transport an aqueous fluid from the soil by capillary action; (ii) exposing a solar absorber comprising a photothermal material loaded on a porous material and in fluid connection with the at least one fluid capillary channel to solar irradiation to generate heat so that evaporation of the aqueous fluid is accelerated and contaminants from the soil are retained by the at least one fluid capillary channel and/or the solar absorber.

[00039] The process may further comprise condensing evaporated water derived from the aqueous fluid into liquid water and returning the latter to the soil.

[00040] The remediation apparatus and the process disclosed herein are applicable to any soil type that may contain contaminants and has capillary flow to the remediation apparatus. This means the soil shall have small pore size for high capillary rise. The remediation apparatus and the process disclosed herein may find application in soils such as sandy soils, clay soils, silty soils, peaty soils, chalky soils, and loamy soils. In some embodiment, the contaminated soil is sandy soil.

[00041] The remediation apparatus and the process disclosed herein are especially suited for use in moist soil because the apparatus relies on transport of contaminants into the apparatus in water. In this regard, it is desirable for the soil to have a relatively high moisture content, for example >30wt%, so that the soil can display good maximum water holding capacity, which enables the apparatus and the process disclosed herein to work effectively. If needed, a water reservoir such as a water tank can be used to add water into soil so as to supply an aqueous fluid that has trapped the contaminants from the soil which is to be treated by the remediation apparatus disclosed herein. An experimental example of the remediation apparatus with a water reservoir is given in Figure 2. It is also possible for the water reservoir to serve as the water collector described herein.

[00042] The contaminants to be removed from soil may include heavy metal ions, organic pollutants, endocrine disrupting chemicals (EDC), and particulate matters. The heavy metal ions can include, but are not limited to, As ³⁺ , Pb ²⁺ , Cu ²⁺ , Cd ²⁺ , Cr ³⁺ , Zn ²⁺ and Hg ²⁺ . The organic pollutants can include, but are not limited to, coomassie brilliant blue, rhodamine B, congo red, methylene blue, Aldrin, Atrazine, Chlordane, Chlorpyrifos, Chlordecone, Decabromodiphenyl ether, Dicofol, DDT, Dieldrin, 2,4-D, Endrin, Glyphosate, Heptachlor, Hexachlorobenzene (HCB), Hexabromobiphenyl, Hexabromodiphenyl ether, Heptabromodiphenyl ether, Alpha hexachlorocyclohexane, Beta hexachlorocyclohexane, Hexabromocyclododecane, Hexachlorobutadiene, Lindane, Mirax, Toxaphene, Pentachlorobenzene, Pentachlorophenol, Polychlorinated biphenyls (PCB), Polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated naphthalenes, short-chain chlorinated paraffins, tetrabromodiphenyl ether, pentabromodiphenyl ether, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and Polychlorinated dibenzofurans (PCDF). In some further embodiments, the endocrine disrupting chemicals are selected from, but not limited to, Lead, Phthalates, Cadmium, Dioxins, Bisphenol A (BP A), Phthalates, Phenol, Brominated Flame Retardants, Polychlorinated biphenyls (PCBs), Parabeans, UV Filters, Triclosan, and Perfluorochemicals. In some further embodiments, the particulate matters are selected from, but not limited to, microplastics. The microplastics mentioned herein refers to plastic debris <5 mm in size. Preferably, the solar driven biomimetic in-situ remediation apparatus of the disclosure is used to remove Pb ²⁺ , PFOS, and/or PFOA.

Fluid capillary channels

[00043] The fluid capillary channels are in fluid connection with an aqueous fluid contained in a contaminated soil and are configured to spontaneously draw in and transport an aqueous fluid from a contaminated soil by capillary action and to the solar absorber under solar irradiation. To this end, they may take the form of capillary channels. [00044] It is possible for a length part of the fluid capillary channel(s) to be above the surface of soil and another length part of the fluid capillary channel(s) to be under the surface of soil. In this case, the length part of the fluid capillary channel/ s) above the surface of soil together with the solar absorber, functions similar to the shoots of a plant, while the length part of the fluid capillary channels under the surface of soil, functions as roots of a plant. It is believed that the part of the fluid capillary channel(s) functioning similar to the shoots of a plant should not be too high as capillary action may not be sufficient to raise the water to the solar absorber. In certain embodiments, for the purpose of good contact and ability to extract water from soil, at least 5 cm depth might be necessary for the part of the fluid capillary channel(s) functioning as roots of a plant.

[00045] The plurality of fluid capillary channels may be provided by a porous sponge. As used herein, the term “sponge” means a porous material having interconnected open cells. Figure 3 shows open cells contained within PEC coated sponge, which serve as the fluid capillary channels for the present disclosure. The porous sponge may have an average pore size range of between tens of nanometres to mic of micrometers. It is believed that the average pore size should be small enough to promote capillary action, but should not be too small to get clogged or jeopardise adsorption capacity for some contaminants. The porous sponge may have a porosity of 50 to 95%. In some embodiments, the porous sponge can be formed from any suitable hydrophilic porous material such as melamine sponge, cellulose sponge, carbon sponge, cotton rod, cloth roll, and porous hydrogels. In other embodiments, the sponge can be formed from porous hydrophobic materials coated with a hydrophilic surface layer, e.g. porous polyurethane coated with a hydrophilic polydopamine layer. In some further embodiments, the sponge can be a natural sponge, such as honeycomb natural sponge.

[00046] The porous sponge may be formed from an adsorbent material or the porous sponge may be a non-active sponge support material having an adsorbent material coating. The non-active sponge support material may be those sponges outlined above. It is desirable for the adsorbent material to be used herein to be low toxic, hydrophilic, porous and/or of high adsorption capacity. The adsorbent material used herein is selected from, but not limited to, polyelectrolyte complex (PEC), sodium alginate and hydroxyapatite. Known methods are suitable for applying an adsorbent material coating onto the sponge support material, for example, by immersion or by casting. In certain specific embodiments, the adsorbent material is a poly electrolyte complex (PEC). The PEC may be selected from PDopa-PAH PEC and chitosan-based PEC. For example, the PEC sponge is a PDopa-PAH PEC prepared from poly(allylamine hydrochloride) (PAH) and poly (L-3,4-dihydroxyphenylalanine) (PDopa). The preparation method thereof can be found, for example, in Yu, L., Liu, X., Yuan, W., Brown, L. J. &

Wang, D. Confined Flocculation of Ionic Pollutants by Poly(L-dopa)-Based Polyelectrolyte Complexes in Hydrogel Beads for Three-Dimensional, Quantitative, Efficient Water Decontamination. Langmuir. 31, 6351-6366 (2015). PECs may be particularly suitable for adsorbing or binding to heavy metal ions present in the soil. In other specific embodiments, the adsorbent material is sodium alginate. The nontoxicity and high biodegradability of sodium alginate could make the adsorbent material environmentally friendly.

[00047] For the purpose of the present disclosure, the sponge or the pore surfaces inside the sponge need to be relatively hydrophilic to induce strong capillary action. In this regard, a water dropping test with a result of adsorption in <1 second may be considered in choosing a suitable sponge. It is also desirable for the sponge to have ability to adsorb and retain a large volume of water, so that it stays moist and resupplies the evaporation surface. Furthermore, the sponge is required to be thermally stable, non-toxic and have good adsorption capacity for targeted contaminants. In some embodiments, a melamine sponge with a PDopa-PAH PEC coating is used as the porous sponge.

Solar absorber

[00048] It is desirable for the solar absorber to realise full-spectrum solar-to-heat. In other words, the solar absorber ideally has a relatively wide absorption wavelength. Furthermore, it is desirable for the photothermal material used for the solar absorber to have satisfactory photothermal conversion efficiency. The aqueous fluid is transported to the upper surface of the photothermal material via the fluid capillary channels under capillary forces and solar irradiation. The photothermal material can efficiently absorb sunlight and convert it into heat for evaporating water from the aqueous fluid, which leads to contaminants in the aqueous fluid being left within the remediation apparatus. Figure 4 shows a comparison of solar absorbance of sponge, PECs sponge and RGO-PECs sponge, which suggests that solar absorbance of the solar absorber disclosed herein, i.e. RGO-PECs sponge, is significantly higher than that of sponge, particularly over the visible light spectrum.

Photothermal material

[00049] Generally, any combination of a photothermal material with an appropriate porous material that can accelerate water evaporation from the aqueous fluid may be used. Factors such as light absorption ability and light-to-heat conversion efficiency of a photothermal material as well as appreciable fluid channels and low thermal conductivity of the porous material are likely to play a role in choosing a photothermal material and a porous material.

[00050] Detailed description of photothermal materials can be found in, for example, Xuan Wu, George Y. Chen, Gary Owens, Dewei Chu, Haolan Xu Photothermal materials: A key platform enabling highly efficient water evaporation driven by solar energy, Materials Today Energy, Volume 12, June 2019, pages 277-296. The photothermal material used herein can include, for example, plasmonic metal, such as gold; nanomaterials such as nanospheres, nanowires, nanostars or nanorods; graphene nanosheets; carbon nanotubes; carbon particles; carbon black; carbon nanofibers; silver nanomaterials such as nanospheres, nanowires or nanorods; copper materials such as CuO, CuS (see e.g. X. Wu, M. E. Robson, J. L. Phelps, J. S. Tan, B. Shao, G. Owens and H. Xu, Nano Energy, 2019, 56, 708-715), Cu _x S _y , CuSe, Cu _x Se _y , CuFeS ₂ nanospheres, nanoplates, nanowires, nanoleaves; CuS/Se/Te nanoparticles; CuO hollow spheres, for example those described in J Xu, X Li, X Wu, W. Wang, R Fan, X Liu, H Xu, Journal of Physical Chemistry C 120 (23), 12666-12672, and G. Chen et al, Scientific Reports 2017, 7, 41895; iron oxide materials such as nanospheres, nanowires, or nanorods; polydopamine films and particles, for example those described in H Xu et al., Chemistry of Materials, 2011, 23 (23) 5105-5110, W Xuan et al., Advanced Sustainable System, 2017, 1, 1700046; polypyrrole; nickel, nickel oxide; nickel-cobalt alloy (see B. Shao, Y. Wang, X. Wu, Y. Lu, X. Yang, G. Y. Chen, G. Owens and H. Xu, J. Mater. Chem. A, 2020, 8, 11665-11673), cobalt, cobalt oxide such as Co ₃ 0 ₄ ; manganese, manganese oxide; titanium oxide (Ti ₂ 0 ₃ ), titanium nitride (TiN), TiO; MXene nanostructures; and mixtures of any of the aforementioned photothermally active substances.

[00051] In some embodiments, consideration can be given to carbon-based photothermal materials because of their black colour, low cost, chemical and physical stability, and easy fabrication. By way of example, carbon-based photothermal materials that can be used for the present disclosure include, but are not limited to, graphene oxide (GO), reduced graphene oxide (RGO), graphite, carbon nanotubes (CNT), biomass carbon and carbon black nanoparticles. Carbon-based materials, including carbon black, graphite, carbon nanotubes, and graphene are well-known photothermal materials with broad light absorption that covers the whole solar spectrum. If needed, hybridization of photothermal materials can be adopted to optimise the optical property in both absorption range and intensity.

[00052] In some embodiments, consideration can be given to semiconductor-based photothermal materials, such as nano scaled copper sulphides, cobalt oxide, and molybdenum nitride.

[00053] As discussed above, before loading onto the porous material, the photothermal material can be pre-formed into nanofillers such as nanospheres, nanowires, nanostars or nanorods, nanoleaves, nanosheets. The photothermal material can be loaded onto the porous material by self-polymerization, spray coating, drop casting, dip coating, layer-by-layer (LBL) assembly deposition, chemical vapour deposition, physical vapour deposition, or combinations thereof. In some embodiments, the photothermal material is loaded as a coating onto the porous sponge, for example onto at least one side of the porous sponge that is directed towards solar irradiation when the apparatus is positioned in situ. For this purpose, agarose or the adsorbent material described herein (such as sodium alginate) may be used to prompt adhesion of the photothermal material onto the porous sponge.

[00054] If needed, a layer of hydrophilic polymer/surfactant coating can be applied to the photothermal material. Such coating may be helpful for dragging water through the pores and channels and form a thin water film on the surface of photothermal materials, and thereby enhancing water evaporation rate when exposed to light energy. [00055] Alternatively, a layer of non-fouling coating can be applied to the photothermal material. Such coating may be helpful in preventing adhesion of contaminants including salt and organisms to the photothermal material. Examples of suitable coatings include zwitterionic coatings, and nanoparticle coatings such as Ag, etc.

Porous material

[00056] The porous nature of the porous material means that some aqueous fluid moves through the pores from the fluid capillary channels by capillary action and evaporates from a surface part of the photothermal material or the porous material. As discussed, the photothermal material can generate heat when it is exposed to light. The generated heat then accelerates the evaporation.

[00057] For the purpose of the present disclosure, the porous material is at least partially hydrophilic. For instance, the porous material may have a gradient structure of being hydrophilic at the water supply and being more hydrophobic near the evaporation surface. The porous material can also transfer water to the height of a photothermal evaporation surface. The water supply through the porous material should be equal or more than evaporated water from the photothermal surface and side surfaces of the fluid capillary channels.

[00058] In certain embodiments, the porous material is a porous sponge. In certain embodiments, the porous sponge used for the solar absorber is the same as that used to form the fluid channels. The sponge can be formed from any suitable material as is known in the art, such as melamine sponge, cellulose sponge, carbon sponge, cotton rod, cloth roll, porous hydrogels; porous hydrophobic materials coated with a hydrophilic surface layer, e.g. porous polyurethane coated with a hydrophilic polydopamine layer; and a natural sponge, e.g. honeycomb natural sponge. As with the porous sponge used for the fluid capillary channels, the porous sponge used for the solar absorber may comprise an adsorbent material having an affinity for one or more contaminants present in the soil. The porous sponge may be formed from the adsorbent material or the porous sponge may be a non-active sponge support material having an adsorbent material coating. It is desirable for the adsorbent material to be low toxic, hydrophilic, porous and/or of high adsorption capacity. The adsorbent material used herein is selected from, but not limited to, a polyelectrolyte complex (PEC), sodium alginate and hydroxyapatite. It is possible to apply a solution of the adsorbent material onto the sponge support material (for example, by immersion or by casting) to form an adsorbent material coating. In some embodiments, the adsorbent material is a poly electrolyte complex (PEC). The PEC may be selected from PDopa-PAH PEC and chitosan-based PEC. In some specific embodiments, the PEC sponge is a PDopa-PAH PEC prepared from poly(allylamine hydrochloride) (PAH) and poly (L-3,4-dihydroxyphenylalanine) (PDopa) which is optimised for application. Preparation methods thereof can be found, for example, in Yu, L., Liu, X., Yuan, W., Brown, L. J. & Wang, D. Confined Flocculation of Ionic Pollutants by Poly(L-dopa)-Based Polyelectrolyte Complexes in Hydrogel Beads for Three-Dimensional, Quantitative, Efficient Water Decontamination. Langmuir. 31, 6351-6366 (2015). PECs may be particularly suitable for adsorbing or binding to heavy metal ions present in the soil. In other specific embodiments, the adsorbent material is sodium alginate. The nontoxicity and high biodegradability of sodium alginate makes it environmentally friendly.

[00059] In certain embodiments, RGO is used as the photothermal material, and a melamine sponge with a PDopa-PAH PEC coating is used as the porous sponge for the solar absorber. In this case, RGO can be coated onto the sponge for the solar absorber, for example, by drop casting. Furthermore, it may be preferable that the PDopa-PAH PEC coated sponge used for the solar absorber is the same as that for the fluid capillary channels and the fluid capillary channels are interconnected open cells within the PDopa- PAH PEC coated sponge.

Water collector

[00060] The remediation apparatus may further comprise a water collector in fluid connection with evaporated water generated by the solar absorber. The water collector is configured to condense water vapour generated from the solar absorber into liquid water and return the latter to the soil so that less water is needed to maintain operation of the remediation apparatus disclosed herein.

[00061] The water collector may comprise a condenser configured to transform evaporated water into liquid water. An effluent from the water collector can be used to irrigate the soil to keep the soil at desirable humidity.

[00062] In an embodiment, the water collector is in the form of a transparent enclosure surrounding the solar absorber. Water vapour from the solar absorber contacts the inner surface of the enclosure where it is cooled and condenses to form water which then runs down to the lower portion of the enclosure. One or more outlets in a lower portion of the enclosure direct condensed water back into the soil adjacent the remediation apparatus.

[00063] If there is no water collector as part of the remediation apparatus, a greenhouse plastic film surrounding the apparatus may function to condense water vapour generated from the solar absorber into liquid water and the latter can drop or flow back to the soil (see Figure 9). Alternatively, or in addition, the remediation apparatus may be operated with the aid of a water reservoir such as water tank (see Figure 2). The water reservoir is to supply an aqueous fluid to keep the soil at desirable humidity.

Operation of the apparatus

[00064] The apparatus described herein can be put into use by simply burying part of the fluid capillary channel(s) in contaminated soil. The apparatus will automatically work upon solar irradiation. (Figure 2, Figure 7a and Figure 9). In an embodiment shown in Figure 9, the remediation apparatus is placed inside a greenhouse. The transparent greenhouse plastic film enclosing the remediation apparatus functions similar to a water collector, which condenses water vapour generated from the solar absorber into liquid water and return the latter to the soil so as to allow automatic operation of the apparatus. The aqueous fluid travels through the fluid capillary channels and the solar absorber by capillary action under solar irradiation, during which contaminants from the soil are retained by the at least one fluid capillary channel and/or the solar absorber. Water vapour from the solar absorber is cooled when contacting the inner surface of the greenhouse plastic film and condenses into liquid water, and then flows back to the soil for reuse.

[00065] The contaminants are transported with the extracted water from the soil into specific components of the apparatus such as the fluid capillary channels, the porous material and the photothermal material, where the contaminants may be locked by the adsorbent material. Once the capillary channels and photothermal evaporation surfaces reach their adsorption capacity to the contaminants, they can either be replaced by new unexposed materials or, if economically valuable, recovered by regeneration of the component materials. Regeneration can be done with acidic solutions. Alternatively, the used component materials can be treated via incineration to concentrate the waste further.

[00066] The apparatus can work under different conditions, even without sunlight. In the absence of sunlight, the natural water evaporation with a relatively slow evaporation rate still can drive the soil remediation. Rainfall can reflux alkaline cation ions such as Na ⁺ , K ⁺ to the soil while the heavy metal ions are kept in the apparatus by the adsorbent material disclosed herein.

[00067] The remediation apparatus can achieve highly efficient remediation much better than phytoremediation without being subjected to phytotoxicity. In addition the evaporation rate is much faster than the one typically observed in plants so that the overall remediation rate is much faster.

EXAMPLES

Fabrication of the apparatus

[00068] Example 1: RGO-PECs loaded sponge and fabrication of the apparatus

[00069] The overall synthesis of an RGO-PECs sponge is depicted in Figure 5. Poly electrolyte complexes (PECs) were prepared via simply mixing of aqueous solutions of poly(L-3,4- dihydroxyphenylalanine) (PDopa) and PAH in a 3.5: 1 molar ratio as previously reported. The preparation method thereof can be found, for example, in Yu, L., Liu, X., Yuan, W., Brown, L. J. & Wang, D. Confined Flocculation of Ionic Pollutants by Poly(L-dopa)-Based Polyelectrolyte Complexes in Hydrogel Beads for Three-Dimensional, Quantitative, Efficient Water Decontamination. Langmuir. 31, 6351-6366 (2015). An aqueous suspension (200 luL) of the as-prepared PECs was warmed to 70 °C with stirring (500 r minute ¹ ) on a water bath, and agarose (3 g) was then added. Subsequently, after the agarose was completely dissolved, the hot homogenous suspension was drop cast onto a melamine sponge to give a PECs loaded sponge. Briefly, the top layer was the absorber layer having a diameter of 4 cm and a thickness of 1 cm. Three rectangular cuboid sponges with an area 1.0 x 1.0 cm ² and a height of 9 cm were used as the fluid channels for water and ions transpiration during evaporation. These three rectangular cuboids were evenly distributed along the edge of the upper layer. In addition, to enhance solar light adsorption, whilst the agarose was still warm, an aqueous RGO solution (1 mg mL ¹ ) was also drop cast into the sponge surface to form an RGO-PECs coated sponge. The obtained sponge was cooled to facilitate gelation prior to freeze drying (-60 °C, 0.018 mbar) for 48 hours. As can be seen, the melamine sponge with the PDopa-PAH PEC coating is used for both the solar absorber and the fluid capillary channels.

[00070] Example 2: RGO-Sodium alginate (SA) sponge and fabrication of the apparatus

[00071] The overall synthesis of the rGO-SA sponge is shown in Figure 10a. A melamine sponge was initially immersed in a 5% aqueous sodium alginate solution for 6 hours to ensure complete incorporation of the solution throughout the sponge matrix. Thereafter the sodium alginate treated sponge was freeze dried and then immersed into a 5% CaCl ₂ solution for another 6 hours to promote crosslinking. The crosslinked alginate sponge was then washed thoroughly with Milli-Q water and again freeze dried to obtain the final SA coated sponge.

[00072] Then, an aqueous RGO-SA solution (1 mg mL ¹ RGO and 5% SA) was loaded on to the surface of the SA coated sponge. In this step, the SA-coated sponge was initially immersed into 0.1% CaCl ₂ before the mixture of RGO and SA were coated on the surface of the SA coated sponge. The RGO- Sodium alginate sponge was then freeze dried and again immersed into 5% of CaCl ₂ for another 6 horns to crosslink the surface. The final synthesized sponge was washed using Milli-Q water and dried prior to use.

[00073] While loading the sponge with SA mainly improved Pb adsorption, coating the top surface of the sponge with rGO significantly increased light absorption to >96% in the wet state (Figure 10b). In addition, the rGO-SA sponge also exhibited excellent hydrophilicity as determined by a water contact angle test. The lower sodium alginate loaded subsurface adsorbed water quickly, within 0.2 s, where fast water adsorption is beneficial for enhanced water transport. For the upper surface layer, incorporating both S A and rGO, the adsorption of water was relatively slow, with complete water adsorption taking about 0.9 s (Figure 10c). In addition, the entire rGO-SA sponge could also adsorb a large amount of water. The initial rGO-SA sponge weighed 0.18 g, and the weight increased > 63-fold to 11.37g after only 2s of water adsorption. SEM images of the untreated sponge showed that the unmodified sponge initially had a relatively uniform porous structure (Figure lOd), while after coating with SA, the pores became filled with SA (Figure lOe).

[00074] Example 3: rGO@«-HAP@Alg cellulose sponge and fabrication of the apparatus

[00075] A cellulose sponge loaded with «HAR (hydroxyapatite), Alg and coated with rGO was fabricated as an artificial evaporator (rGO@/?HAP@Alg cellulose sponge) using the fabrication process illustrated in Figure 1 la. The «HAPri Alg cellulose sponge was composited by casting the «HAPri Alg solution onto the cellulose sponge. The «HAP ri Alg gelation and loading was conducted by immersion in a CaCl ₂ solution followed by freezing drying (Figure 1 la steps 2-3). Loading of the cellulose sponge with rtHAP A Alg changed the morphology of the cellulose sponge (Figure 1 lb-c). Before loading, a smooth surface can be clearly observed (Figure lib). However, after loading, the surfaces of sponge were occupied with composite (Figure 1 lc). High-resolution SEM images revealed that «HAR adhered on the sponge surfaces (Figure lid). Subsequently, after coating with rGO, the cellulose sponge surface became rougher and more wrinkled (Figure 1 le). Roughness can enhance light absorption for light-to-heat conversion and increase the evaporation surface area. In addition, the rGO@/?HAP@Alg cellulose sponge was extremely hydrophilic, exhibiting immediate water adsorption (Figure 1 If). Capillary water rise tests also showed that the rGO@«HAP@Alg cellulose sponge had a high water transpiration ability, where the theoretical ascent height was increased from 11.3 cm (pristine cellulose sponge) to 26.8 cm (rGO@/?HAP@Alg cellulose sponge) (Figure 1 lg). The high water transpiration ability was attributed to the hydrophilic properties of sodium alginate. In addition, compared to the pristine sponge, the rGO@/?HAP@Alg cellulose sponge was highly stable and exhibited no obvious shape change when contacted with water. To realize a biomimetic structure, the fabricated functional cellulose sponge was divided into three different functional areas. This included upper, middle, and bottom layers corresponding to roots, stems and leaves, respectively. The root part was modified by cutting to resemble a real plant root structure, which was suspected of enhancing water and ion capture. A biomimetic evaporator was formed by simply rolling the sponge into a cylinder. The leaf part, having different leaf numbers, was simply cut to obtain the different target leaves number while maintaining the same top surface area (Figure 1 lh). The surface of the leaf structure was coated with rGO to enhance light absorption. In addition, with rGO incorporated, the wet state light absorption ability increased significantly from 68.5% (cellulose) and 62.8% («HAP@Alg cellulose sponge) to 96.3% (rGO@/?HAP@Alg cellulose sponge).

Evaporation performance

[00076] Evaporation performance of the remediation apparatus (or the photothermal material loaded on the porous material) can be measured by the weight loss of the soil vs time. The evaporation rate is measured by water loss by weight and area under 1 sun illumination over time. Figure 6a shows that the evaporation rate of RGO-PECs sponge is clearly faster than that of PECs sponge and sponge. In certain embodiments, the evaporation rate of water from the photothermal material loaded on the porous material is greater than 1.0 kg m ² h ¹ under 1.0 sun illumination. The amount of evaporation increases with the increase in height of the evaporator sponge (see Figure 6b), which corresponds to the length part of the fluid capillary channel(s) above the surface of the soil together with the solar absorber and functions similar to the shoots of a plant. The contribution of the capillary channel(s) in water evaporation may be greater than the photothermal surface when the capillary channel(s) reaches a certain height. For instance, the turning point of contribution occurs when the height of the evaporator sponge in Figure 6c is greater than about 3 cm. For Figure 6c, “Blank” represents dark evaporation, and it can be seen that when the height of the evaporator sponge is less than about 3 cm, the dark evaporation is less than the evaporation under 1 sun illumination. The side surface of the capillary channel(s) also contributes to evaporation rate (see Figure 6d). In practical application, wind will further significantly improve the overall evaporation rate.

[00077] Figure 7c shows that the remediation apparatus fabricated from RGO-PECs sponge exhibits consistent long-term evaporation rates over at least 14 days (see Figure 7c). In Figure 7c, the darker shaded areas denote dark periods without illumination and the light areas indicate illuminated periods. Figure 7c also suggests that even without sunlight, the apparatus still can deliver an evaporation rate > 0.4 kg m ² h ¹ .

[00078] Under 1 sun illumination, the evaporation rate for the soil only, unmodified sponge, SA sponge, and rGO-SA sponge were 0.35, 0.54, 0.49 and 0.78 kg m ² h ¹ respectively (Figure 12a). Compared with unmodified sponge, the SA sponge has a lower evaporation performance probably due to the fact that some of the pores on the sponge surfaces were filled with SA (Figure lOe), slowing the escape of the vapour from the evaporation surfaces. A slightly lower dark evaporation rate of the SA sponge relative to unmodified sponge was also observed. The rGO-SA sponge showed the best performance in solar evaporation of soil water due to the photothermal effect from the rGO coating. Thus, under 1 sun illumination, the evaporation performance of the rGO-SA sponge in soils having different soil water content (Figure 12b) indicated that while evaporation rate increased as water content increased from 20 to 30%, the relative improvement in evaporation rate was not always directly proportional to the increase in soil water content. For example, the evaporation rate increased only slightly when the soil water content was relatively high (25-30%) indicating that when the soil water content reached the maximum water holding capacity, there was adequate water supply to the sponge surface and evaporation rate was thereafter not affected by moisture content.

[00079] The variation in the relative contributions of solar intensity and wind velocity (Figure 12c) showed that the evaporation rate increased from 0.78 to 3.6 kg m ² h ¹ as solar intensity increased from 1 to 5 sun, while the increase in evaporation from 0.78 to 1.81 kg m ² h ¹ as wind velocity increased from 0 to 2 m s ¹ under 1 sun illumination was more modest. Under 1 sun illumination, the temperature of the top evaporation surface increased rapidly due to its excellent photothermal effect (Figure 12d and e). When the soil water content was 30%, the average evaporation surface temperature increased rapidly from 24 to 28 °C within 5 minutes, was stable at 34°C after 30 minutes (Figure 12d).

[00080] Practical natural solar evaporation of soil water was evaluated in outdoor experiments in the daylight hours fromlO am to 6 pm. The environmental temperature and solar flux were recorded using light intensity and temperature meters (Figure 13a). Different from the indoor tests, during the outdoor experiment, solar incident-angle and light intensity varied with sun position, leading to variation in evaporation rate (Figure 13b). Long-term outdoor tests (12 days) showed that evaporation rate for the rGO-SA sponge can be maintained between 0.8 and 1.4 kg m ² h ¹ except for 3 rainy days (Days 3, 8, and 10) (Figure 13c). These results demonstrated that rGO-SA sponge based solar evaporators are well suited for real-world solar evaporation of soil water.

[00081] Compared with raw cellulose sponge, rGO@/?HAP@Alg cellulose sponge had a higher evaporation performance, which increased from 1.42 to 1.91 kg m ² h ¹ with 3 leaves and 2 cm height (Figure 14a). Moreover, rGO@/?HAP@Alg cellulose sponge had a higher surface temperature under 1.0 sun illumination. The effect of stem height on solar evaporation rate was also evaluated, where under dark evaporation, the evaporation rate was proportional to the height. Increasing stem height can contribute to improved water evaporation because of the increase in the dark evaporation surface area. However, under illumination, the evaporation rate increased slowly when the stem height was greater than 3 cm (Figure 14b). Thus, increases in stem height did not significantly improve the evaporation rate and moreover when the stem was too high there was insufficient water supply to the leaf surface and the evaporation rate consequentially declined. While just 3 leaves exhibited a relatively high evaporation rate, the evaporation rate could be further improved by optimizing leaf number. Inspired by the tree’s leaf structure, evaporators with the same mass and volume of the materials; but different leaf numbers were fabricated. Compared with 3 leaves, increasing leaf number could be a promising way to improve evaporation performance due to increasing side evaporation surfaces. For example, the 3 leaf evaporator had a side evaporation surface of 4.80 cm ² compared to a 24 leaf evaporator with an additional external 25.20 cm ² . Under dark evaporation, as leaf number increased from 3 to 24, the evaporation rate increased from 0.78 to 1.59 kg m ² h ¹ . Under 1.0 sun illumination, the evaporation rate increased from 2.21 kg m ² h ¹ (3 leaves) to 3.10 kg m ² h ¹ (24 leaves), which is much higher than most biomimetic structures previously reported (Figure 14c). When the leaf number was 24, the average temperature of the leaves increased to 24.1°C within 5 minutes and remained constant thereafter with only slight fluctuations (Figure 14d). When the leaf number was increased from 3 to 12, the average temperature of the leaves decreased from 25.8 to 24.6 °C (Figure 14e). Soil remediation

[00082] Reduction of mobile contaminant fractions in the soil can be determined by the Tessier sequential extraction procedure. The procedure is used to quantify the types of “speciation” of metals in a soil by associating it with the particular fraction it is partitioned into. This involves sequential extraction using a variety of different extraction media and then determination of the metal content in that extracted fraction by inductively coupled plasma - optical emission spectrometry (ICP-OES) for the purpose of the present disclosure.

[00083] Pb fractions in the soil were evaluated herein according to the sequential extraction procedure (Tessier, A., Campbell, P. G. C. & Bisson, M. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51, 844-851 (1979)). The Tessier sequential extraction method was used to analyze the heavy metal fractions, which were divided into five types: exchangeable (FI), carbonate-bound (F2), Fe/Mn oxide-bound (F3), organic matter-bound (F4), and residual fraction (F5) (see Figure 8(b)). Prior to initiating sequential extraction, and after each extraction step, soil samples were air-dried and sieved < 2 mm. After each sequential extraction, the total HM content in the extract solution was analyzed by ICP-OES. Each batch of samples included blanks and duplicate. The extraction procedure is provided in Table 1.

[00084] Table 1 - Extraction procedure for Pb fractions in soil

[00085] Taking Pb ²⁺ as an example, Pb ²⁺ in the soil can be reduced from 432 mg/kg to 352mg/kg after 14 days by use of a remediation apparatus fabricated from the RGO-PECs loaded sponge prepared above. The bioavailable Pb fraction was reduced from 359 to 221 mg/kg (38.4%) after 14 days by use of a remediation apparatus fabricated from the RGO-PECs loaded sponge prepared above.

[00086] The concentrations of contaminants adsorbed in the various parts of the apparatus were calculated through acidic digestion of the fluid(s) and the solar absorber and then quantification of the metal content by inductively coupled plasma - mass spectrometry (ICP-MS) and/or ICP-OES. The results in relation to Pb ²⁺ in Figure 8(c, d) are obtained in this way. For solar-based remediation, Root means the length part of the fluid capillary channel(s) under the surface of soil and Shoot means the length part of the fluid capillary channel(s) above the surface of soil together with the solar absorber. For phytoremediation, Root and Shoot respectively means plant roots and shoots after growth.

[00087] For the rGO-SA sponge, after 12 days evaporation, the efficiency of Pb extraction from the soil was evaluated. Without solar illumination, compared to the unmodified sponge the rGO-SA sponge increased the adsorption ability by 69.2% from 1.72 to 2.91 mg g . Under one sun illumination, the adsorption ability of the rGO-SA sponge further increased to 3.56 mg g (Figure 15a). This was because with solar illumination, the evaporation rate was enhanced, which improved transpiration rate, leading to the observed higher Pb adsorption. Compared with indoor evaporation, outdoor solar evaporation further increased the Pb adsorption ability by 48.9% from 3.56 to 5.30mg g for the rGO-SA sponge (Figure 15a). The Tessier sequential extraction showed that when the rGO-SA sponge is utilized, changes in the Pb fraction in the soil occurred after solar driven evaporation and both the total Pb and exchangeable Pb fractions (FI) were decreased (Figure 15b). Compared with the in-door test, the outdoor test had a higher removal rate of FI, confirming that this rGO-SA sponge was suitable for practical outdoor soil Pb remediation.

[00088] Long-term soil remediation performance was evaluated using solar driven evaporation remediation (SDER). After 4 weeks illumination, heavy metal (HM) content of the soil porewater decreased after treatment (Figure 16). In the control soil, the HM content in the porewater was 1.325, 0.253, 0.420, 0.113, 0.278 mg kg for As, Cd, Cr, Pb, and Zn respectively. Whereas, after SDER treatment, HM content in porewater was obviously decreased to 0.743, 0.173, 0.215, 0.045, and 0.205 mg kg ¹ for As, Cd, Cr, Pb, and Zn, respectively. The removal rate thus reached 44.0, 31.7, 48.8, 60.0, and 26.1% for As, Cd, Cr, Pb, and Zn, respectively, which would contribute to a significant decrease in overall risk due to HM toxicity.

[00089] It is suggested by the above experimental results that the solar evaporation-based soil remediation disclosed herein possesses significant advantages in remediation efficiency over the phytoremediation. [00090] Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and variations such as "comprises" and "comprising" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers.

[00091] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[00092] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the disclosure as set forth and defined by the following claims.