Boosting extraction of Pb in contaminated soil via interfacial solar evaporation of multifunctional sponge

Interfacial solar water evaporation is a reliable way to accelerate water evaporation and contaminant remediation.Embracing the recent advance in photothermal technology,a functional sponge was prepared by coating a sodium alginate(SA)impregnated sponge with a surface layer of reduced graphene oxide(rGO)to act as a photothermal conversion medium and then subsequently evaluated for its ability to enhance Pb extraction from contaminated soil driven by interfacial solar evaporation.The SA loaded sponge had a Pb adsorption capacity of 107.4 mg g^(-1).Coating the top surface of the SA sponge with rGO increased water evaporation performance to 1.81 kg m^(-2)h^(-1)in soil media under one sun illumination and with a wind velocity of 2 m s^(-1).Over 12 continuous days of indoor evaporation testing,the Pb extraction efficiency was increased by 22.0%under 1 sun illumination relative to that observed without illumination.Subsequently,Pb extraction was further improved by 48.9%under outdoor evaporation conditions compared to indoor conditions.Overall,this initial work shows the significant potential of interfacial solar evaporation technologies for Pb contaminated soil remediation,which should also be applicable to a variety of other environmental contaminants.

Influence of Indian mustard (Brassica juncea) on rhizosphere soil solution chemistry in long-term contaminated soils:A rhizobox study

This study investigated the influence of Indian mustard （Brassicajuncea） root exudation on soil solution properties （pH, dissolved organic carbon （DOC）, metal solubility） in the rhizosphere using a rhizobox. Measurement was conducted following the cultivation of Indian mustard in the rhizobox filled four different types of heavy metal contaminated soils （two alkaline soils and two acidic soils）. The growth of Indian mustard resulted in a significant increase （by 0.6 pH units） in rhizosphere soil solution pH of acidic soils and only a slight increase （〈 0.1 pH units） in alkaline soils. Furthermore, the DOC concentration increased by 17-156 mg/L in the rhizosphere regardless of soil type and the extent of contamination, demonstrating the exudation of DOC from root. Ion chromatographic determination showed a marked increase in the total dissolved organic acids （OAs） in rhizosphere. While root exudates were observed in all soils, the amount of DOC and OAs in soil solution varied considerably amongst different soils, resulting in significant changes to soil solution metals in the rhizosphere. For example, the soil solution Cd, Cu, Pb, and Zn concentrations increased in the rhizosphere of alkaline soils compared to bulk soil following plant cultivation. In contrast, the soluble concentrations of Cd, Pb, and Zn in acidic soils decreased in rhizosphere soil when compared to bulk soils. Besides the influence of pH and DOC on metal solubility, the increase of heavy metal concentration having high stability constant such as Cu and Pb resulted in a release of Cd and Zn from solid phase to liquid phase.

Chemodynamics of heavy metals in long-term contaminated soils:Metal speciation in soil solution

The concentration and speciation of heavy metals in soil solution isolated from long-term contaminated soils were investigated. The soil solution was extracted at 70% maximum water holding capacity （MWHC） after equilibration for 24 h. The free metal concentrations （Cd^2＋, Cu^2＋, Pb^2＋, and Zn^2＋） in soil solution were determined using the Donnan membrane technique （DMT）. Initially the DMT was validated using artificial solutions where the percentage of free metal ions were significantly correlated with the percentages predicted using MINTEQA2. However, there was a significant difference between the absolute free ion concentrations predicted by MINTEQA2 and the values determined by the DMT. This was due to the significant metal adsorption onto the cation exchange membrane used in the DMT with 20%, 28%, 44%, and 8% mass loss of the initial total concentration of Cd, Cu, Pb, and Zn in solution, respectively. This could result in a significant error in the determination of free metal ions when using DMT if no allowance for membrane cation adsorption was made. Relative to the total soluble metal concentrations the amounts of free Cd^2＋ （3%-52%） and Zn^2＋ （11%-72%） in soil solutions were generally higher than those of Cu^2＋ （0.2%-30%） and Pb^2＋ （0.6%-10%）. Among the key soil solution properties, dissolved heavy metal concentrations were the most significant factor governing free metal ion concentrations. Soil solution pH showed only a weak relationship with free metal ion partitioning coefficients （Kp） and dissolved organic carbon did not show any significant influence on Kp.

Recent innovations in 3D solar evaporators and their functionalities

Interfacial solar evaporation(ISE)has emerged as a promising technology to alleviate global water scarcity via energy-efficient purification of both wastewater and seawater.While ISE was originally identified and developed during studies of simple double-layered two-dimensional(2D)evaporators,observed limitations in evaporation rate and functionality soon led to the development of three-dimensional(3D)evaporators,which is now recognized as one of the most pivotal milestones in the research field.3D evaporators significantly enhance the evaporation rates beyond the theoretical limits of 2D evaporators.Furthermore,3D evaporators could have multifaceted functionalities originating from various functional evaporation surfaces and 3D structures.This review summarizes recent advances in 3D evaporators,focusing on rational design,fabrication and energy nexus of 3D evaporators,and the derivative functions for improving solar evaporation performance and exploring novel applications.Future research prospects are also proposed based on the in-depth understanding of the fundamental aspects of 3D evaporators and the requirements for practical applications.

Porous carbon-based thermally conductive materials:Fabrication,functions and applications

The demand for electronic devices has dramatically increased in the past few years.Efficient electronic devices require excellent thermal management systems to extend their operation time and prevent heat accumulation from affecting performance.Carbonaceous materials are considered as one of the ideal thermal management materials due to their excellent physiochemical stability.In addition,since porous-structured carbon materials typically exhibit outstanding thermal conductivity,low density,and large contact area,they have attracted considerable attention from both academia and industry in the last decades.In this review,methods and strategies for the preparation of highly thermally conductive porous carbon-based materials and the factors that influence their thermal conductivity of the materials are summarized.The thermal performance of porous carbonaceous materials fabricated by different approaches and their applications are also discussed.Finally,the potential challenges and strategies for the development and applications of highly thermally conductive porous carbona-ceous materials are discussed.

Enhancing solar steam generation using a highly thermally conductive evaporator support

Interfacial solar steam generation is an efficient water evaporation technology which has promising applications in desalination,sterilization,water purification and treatment.A common component of evaporator design is a thermal-insulation support placed between the photothermal evaporation surface and bulk water.This configuration,common in 2-dimensional(2 D)evaporation systems,minimizes heat loss from evaporation surface to bulk water,thus localizing the heat on the evaporation surface for efficient evaporation.This design is subsequently directly adopted for 3-dimensional(3 D)evaporators without any consideration if it is appropriate.However,unlike 2 D solar evaporators,the 3 D evaporators can also harvest additional energy(other than solar light)from the air and bulk water to enhance evaporation rate.In this scenario,the use of thermal insulator support is not proper since it will hinder energy extraction from water.Here,the traditional 3 D evaporator configuration was completely redesigned by using a highly thermally conductive material,instead of a thermal insulator,to connect evaporation surfaces and the bulk water.Much higher evaporation rates were achieved by this strategy,owing to the rapid heat transfer from the bulk water to the evaporation surfaces.Indoor and outdoor tests both confirmed that evaporation performance could be significantly improved by substituting a thermal insulator with thermally conductive support.These findings will redirect the future design of 3 D photothermal evaporators.

More from less:improving solar steam generation by selectively removing a portion of evaporation surface

Using minimal photothermal material to achieve maximum evaporation rate is extremely important for practical applications of interfacial solar evaporation technology.In this work,we found that with the increase in the size of evaporation surfaces,the evaporation rate decreased.Both experimental and numerical simulation results confirmed that when the evaporation surface size increased,the middle portion of the evaporation surface acted as a‘‘dead evaporation zone”with little contribution to water evaporation.Based on this,the middle portion of the evaporation surface was selectively removed,and counterintuitively,both the evaporation rate and vapor output were increased due to the reconfigured and enhanced convection above the entire evaporation surface.As such,this work developed an important strategy to achieve a higher evaporation rate and increased vapour output while using less material.

A photothermal reservoir for highly efficient solar steam generation without bulk water

A solid photothermal reservoir is designed to implement solar-steam generation in the absence of bulk water.The photothermal reservoir is composed of a water absorbing core encapsulated by a photothermal reduced graphene oxide based aerogel sheet which absorbs light and converts it into heat thus evaporating the stored water.The photothermal reservoir is able to store 6.5 times its own weight in water,which is sufficient for one day solar evaporation,thus no external water supplement is required.During solar-steam generation,since no bulk water is involved,the photothermal reservoir minimizes heat conduction loss,and maximizes both of the exposed evaporation surface area and net energy gain from the environment,leading to an energy efficiency beyond the theoretical limit.An extremely high water evaporation rate of 4.0 kg m-2 h-1(normalized to projection area)is achieved in laboratory studies over a cylinder photothermal reservoir with a diameter of 5.2 cm and a height of 15 cm under 1.0 sun irradiation.Practical evaluation of the photothermal reservoir outdoors as part of a desalination device demonstrates a similar evaporation rate where the salinity of the clean water produced is lower than 24 ppb.Thus the photothermal reservoir shows great potential for real world applications in portable solarthermal desalination.

Boosting solar steam generation by structure enhanced energy management

Interfacial solar-steam generation is a promising and cost-effective technology for both desalination and wastewater treatment.This process uses a photothermal evaporator to absorb sunlight and convert it into heat for water evaporation.However solar-steam generation can be somewhat inefficient due to energy losses via conduction,convection and radiation.Thus,efficient energy management is crucial for optimizing the performance of solar-steam generation.Here,via elaborate design of the configuration of photothermal materials,as well as warm and cold evaporation surfaces,performance in solar evaporation was significantly enhanced.This was achieved via a simultaneous reduction in energy loss with a net increase in energy gain from the environment,and recycling of the latent heat released from vapor condensation,diffusive reflectance,thermal radiation and convection from the evaporation surface.Overall,by using the new strategy,an evaporation rate of 2.94 kg m^-2 h^-1,with a corresponding energy efficiency of solar-steam generation beyond theoretical limit was achieved.

A cobalt oxide@polydopamine-reduced graphene oxide-based 3D photothermal evaporator for highly efficient solar steam generation

Improving the evaporation rate and energy efficiency of solar steam generation is very important to facilitate real-world applications for clean water production.In this work,Co_(3)O_(4)@polydopamine(PDA)nanoparticles were synthesized and combined with reduced graphene oxide(rGO)to fabricate a new Co_(3)O_(4)@PDA-rGO photothermal aerogel.The obtained pho-tothermal aerogel sheet was thereafter used to prepare both two-dimensional(2D)and three-dimensional(3D)photothermal evaporators for solar steam generation.Due to the excellent light absorption and hydrophilicity of the photothermal aerogel,a high evaporation rate of 1.60 kg·m^(−2)·h^(−1) was achieved for the 2D photothermal evaporator.While for the 3D evaporator,the evaporation rate was dramatically increased to 3.71 kg·m^(−2)·h^(−1) with a corresponding light-to-vapor energy efficiency of 107%.This was attributed to an increased evaporation surface area,decreased energy loss from the top evaporation surface to the environment,and energy gain from the environment on the side evaporation surface.The 3D evaporator also showed excellent practical performance in seawater desalination thus demonstrating great potential for real-world applications.

Evaluation of immobilizing agents as soil quality conditioners in addition to their metal(loid) immobilizing effect

In trace metal (TM)-contaminated agricultural soils,management of TM availability is important for safe crop production.In addition,maintenance or improvement of soil quality is vital for sustainable crop cultivation.Decreased TM phytoavailability and increased soil quality can be achieved by the application of various immobilizing agents to soil,which can supply both macronutrients and organic matter.This study investigated the long-term influences of four common immobilizing agents on soil biogeochemical properties and the phytoavailability of TMs in mixed metal-contaminated soil from a cultivated upland near an abandoned mining site.Lime (L),gypsum (G),fly ash (F),and animal manure-based compost (C) were applied to pots containing contaminated soil,either individually or in combination.After incubation for three years under sequential cultivation of two crops and fallow,soil biogeochemical properties were determined,and Brassica rapa plant bioassay was performed.The phytoavailability of all TMs (both cationic metals and anionic metalloids) remained significantly lower in soils treated with immobilizing agents even after three years,when compared with the no-agent control (CK) soil.In addition,the soil quality was significantly improved by treatment with immobilizing agents.For instance,the C and L+C treatments were the most effective in improving soil physical (bulk density,porosity,and water-resistant aggregate stability),chemical (pH,organic matter,total nitrogen,cation exchange capacity,and plant-available phosphorus,magnesium,and potassium),and biological (microbial biomass carbon and dehydrogenase activity) properties.The improvement of soil properties and lowering of TM bioavailability were also consistent with the most significant increase in B.rapa biomass production observed in the C treatment,followed by the L+C,G+F,L,G,F,and L+G treatments,as compared with that in CK.These results indicate that the function of the TM-immobilizing agent as a soil quality conditioner,in addition to its TM immobilizing effect,should be considered when selecting such agents for agricultural or ecological applications.