| The tension situation of the water-energy relationship seriously restricts the harmonious coexistence of human and ecological environment.In recent years,the solar-driven interfacial evaporation technology has shown promising application prospects.However,the photothermal materials suffer from problems such as high thermal conductivity loss,poor wettability,low water evaporation rate,poor environmental tolerance,high cost,and failure to meet the standard of freshwater quality,which hinders the process of large-scale application.In this paper,lowcost biomass(maize straw,enteromorpha,eggplant,rice husk,rice bran,pine sawdust,bamboo sawdust)was used as the main raw material,and a rich fiber structure was obtained by chemical treatment,and developed a three-dimensional biomass-based photothermal material that is environmentally friendly and has excellent photothermal conversion performance;The effects of reaction parameters and preparation process on the microstructure,photothermal conversion performance,water wettability,surface properties,mechanical properties and other physical and chemical properties of biomass-based photothermal materials were systematically investigated by using modern instrumental analysis,and the constitutive relationships between the physical and chemical properties of biomass-based photothermal materials and photothermal conversion performance were clarified,revealing the evaporation mechanism and the reasons for breaking the evaporation limit;The salt tolerance performance of twodimensional photothermal films and multi-source biomass-based photothermal materials in high-salt wastewater and the salt recovery behavior were investigated,and the salt tolerance mechanism of biomass-based photothermal materials in high-salt wastewater was proposed;A biomass-based photothermal material with integrated adsorption-oxidation function was used,and the combined technology of interface evaporation-adsorption-oxidation was analyzed to compare and study the behavior of organic pollutant adsorption and oxidation in biomass-based photothermal materials.The impact of complex water quality on the combined technology was systematically investigated,and the adsorption and oxidation mechanisms of the system were clarified,achieving the goal of effectively controlling organic matter to meet freshwater standards from the source.The main research contents and findings are as follows.(1)The(nitrogen-doped)maize straw/GO aerogels(GM and GMN)were synthesized by low-temperature self-assembly method and atmospheric pressure drying method using maize straw cellulose and graphene oxide(GO)as the main raw materials.The structure of the aerogel was characterized by means of scanning electron microscope,contact angle,infrared imager and other modern instruments.The effect of the ratio of maize straw to GO and heteroatomic nitrogen doping on the physicochemical structure of the aerogel was determined by examining the ratio of maize straw to GO and the heteroatomic nitrogen doping amount.By changing the interaction between aerogel and water molecule,the performance and mechanism of high efficiency evaporation were studied.The results showed that the best performance of the aerogel prepared when the ratio of corn stover to GO was 1:2 and the urea injection amount was 0.5 g.The ratio of maize straw/GO and the amount of nitrogen doping greatly affected the degree of self-assembly of the precursor hydrogel,which in turn affected the density,porosity and water wettability of the aerogel,where the density of GMN2 aerogel was as low as 7.26 mg cm-3 and the porosity as high as 91.6%;The nitrogen doping and maize straw filled GO network significantly improved the water transport capacity,thermal stability and mechanical properties of the materials,including the compressive strength of GMN2 aerogels up to 16.7 kPa at 70%strain;the evaporation rates of GM4 and GMN2 up to 2.71 and 3.22 kgm-2 h-1 under 1 kW-2 solar irradiation,respectively,attributed to their large roughness and abundant pore structure effectively increases the water-air interface and the aerogel has more weakly hydrogen-bonded intermediate water which in turn reduces the enthalpy of water evaporation;In addition,aerogels have excellent salt resistance and stability,and can effectively remove natural organic matter such as tryptophan,proteoid and humic acid.(2)The enteromorpha/GO aerogels(MFeG)based on enteromorpha and GO were synthesized by hydrothermal self-assembly and precipitation methods.The heat loss of MFeG aerogel to the environment through thermal convection,thermal radiation,and thermal conduction was studied by introducing ambient energy,and the mechanism of efficient evaporation was clarified,while the water purification ability of MFeG aerogel in such as sterilization performance,desalination performance,and simulated organic wastewater was evaluated.The experimental results show that the optical absorption of MFeG aerogel is effectively enhanced by introducing amorphous FeOOH nanoparticles,reaching 97～90%,and the rough thermal interface is beneficial to improve the thermal positioning ability(up to;The closed pore structure formed in the lotus root shaped three-dimensional network structure makes the interior have an air sac and excellent hydrophilicity(440 ms,0°),which is helpful for the system to control heat loss and ensure excellent water transmission ability at the same time;It is found that when the height of the aerogel reaches 55 mm,the lower temperature of the side surface of the aerogel causes the loss of heat convection and heat radiation energy to be converted into energy input,reaching 0.093 W,and achieving an evaporation rate of up to 3.85 kgm-2h-1;In addition,the aerogels exhibit excellent sterilization capability,desalination capability and water purification capability under illumination.(3)Eggplant/PPy-based foams(EC-PPy-MO)were synthesized by modifying polypyrrole(PPy)by oxidative polymerization on the three-dimensional framework of biomass eggplant(EC-PPy-MO).The salt tolerance and salt recovery performance of EC-PPy-MO in high-salt wastewater with different concentrations were evaluated.The results show that the addition of methyl orange template is beneficial to the transformation of PPy from spherical particles into slender tubular structures with an average diameter of 230 nm,and the optimal preparation conditions are as follows:the molar ratio of MO:Fe 3+:Py is 1:10:10,taking the photothermal conversion performance and the water evaporation performance as indicators;The multi-level micro-nanometer structure integrated by tubular PPy and biomass is favorable for the multiple reflections and scattering of internal light,so that the absorption of EC-PPy-MO light is as high as 91%,the evaporation rate is 1.49 kgm-2 h-1,and the evaporation rate of spherical PPy modified foam is only 1.21 kgm-2 h-1;When the salinity of high-salt wastewater is lower than 7 wt%,the multi-level micro-nanometer pore structure in EC-PPy-MO foam is favorable for the convection and diffusion of salt water,promotes the dissolution of salt particles at the photothermal interface,and effectively solves the problems of salt blockage and salt crystallization;When the salinity is higher than 15 wt%,the crystallization and accumulation of salt in the photothermal interface due to the boundary Marangoni effect caused by high concentration salt and localized high temperature can effectively solve the problem of salt blockage under high salinity by increasing the height of the photothermal interface,and achieve a high evaporation rate in 25%salt water(-2.8 kgm-2 h-1).(4)Based on the above ideas,a NCNT/GO/cellulose evaporator with edge crystallization salt was constructed by directed transport of the solution.The nitrogen-doped carbon nanotubes embedded with cobalt particles(Co-NCNT)and GO were used as light absorbers to investigate the effect of the light absorption layer on physical and evaporative properties,and to study the balance point between the water supply performance and the evaporative performance of the evaporative system,as well as the salt recovery behavior.The research results show that the graphite nitrogen in Co-NCNT is conducive to reducing the band gap(0.054 a.u.),the local surface plasmon resonance properties of cobalt nanoparticles,and the rich conjugated π bonds in GO,making Co-NCNT-GO capable of achieving 92%full-spectrum light absorption.The pyridine nitrogen and water molecules in Co-NCNT have high adsorption energy(-9.33 kcal mol-1),which is conducive to improving the wettability of water.The concentration gradient of salt solution produced by different water supply areas plays a decisive role in dividing the interface evaporation area and salt accumulation area.It was found that the salt concentration at the edge of the Co-NCNT-GO photothermal film increases as the water supply area decreases,that is,a small water supply area is conducive to forming a large salt concentration gradient(4:1),but a smaller water supply area cannot meet the water required for interface evaporation.When the ratio of water supply area to photothermal area is 4:2.5,it is conducive to controlling the transport path of salt and crystallizing salt at the edge,with a salt recovery rate of 46.54 g m-2 h-1 and continuous stable evaporation for 108 h,maintaining at 1.44 kg m-2 h-1.(5)Based on the above results,organic biomass such as rice husk,rice bran,Enteromorpha,pine sawdust,bamboo sawdust and maize straw were used as the main raw materials,and ammonium polyphosphate was used as the carbon fixing agent.The effects of biomass structure,pyrolysis temperature,ammonium polyphosphate content,raw material ratio and other factors on the macroscopic volume,water wettability,photothermal conversion performance and water evaporation performance of three-dimensional biomass aerogel were studied.The experimental results showed that the volume shrinkage of maize straw-based aerogel with tubular structure was the smallest(34.6%),the volume saturated moisture content of the aerogel based on bamboo wood chip was the highest(0.96),and the water evaporation rate of the aerogel based on pine sawdust,bamboo wood chip and maize straw was excellent,reaching 3.37～3.84 kg m+-2 h-1(dark evaporation was not deducted).With the increase of pyrolysis temperature(400℃-700℃)for maize straw-based aerogel,the rate of water evaporation increases with the increase of pyrolysis temperature(1.72-2.20 kgm-2 h-1).When the aerogel is completely exposed to the side surface,the rate of aerogel evaporation at 500℃ is the highest(3.37 kg m2 h-1).With the addition of ammonium polyphosphate,the photo-thermal conversion performance increased,but the water wetting performance decreased.The maize straw cellulose with high content needs to be added with hydrophilic sodium carboxymethyl cellulose even though the cellulose has excellent photo-thermal conversion performance but the evaporation rate is lower than 0.79 kgm-2 h-1 due to insufficient water supply;In addition,the designed mountain evaporation unit operates in 20%brine for 81 h and the photothermal surface can be eliminated by reflux despite a small amount of salt crystallization,and effective salt recovery can be achieved in the salt crystallization area.(6)Finally,a three-dimensional nitrogen-rich eggplant-based photothermal catalyst(PCEB)was prepared by activating eggplant-based biochar with potassium citrate,and the desalination and carbon reduction behaviors of PC-EB on high-salt wastewater by evaporation,adsorption and oxidation at the source were investigated to clarify its feasibility of controlling VOC in condensate.The experimental results show that by optimizing the preparation process,the best preparation conditions are as follows:the mass ratio of biomass charcoal to potassium citrate is 1:2,and the pyrolysis temperature is 900℃;it is found that the nitrogen content in PC-EB-900 is as high as 6.7%and has oxygen-containing functional groups such as ether group,carbonyl group and carboxyl group,and the light absorption in the near-infrared region can be increased to～99.1%,and the evaporation rate can reach 1.70 kg m-2 h-1;The saturated adsorption capacity of phenol(APAP)can reach 264.55 mg g-1,the oxidation system of PCEB/PMS/sunlight can increase the reaction rate constant by nearly 2 times(0.1978 min-1),and the removal rate of TOC can be as high as 77%.The increase in temperature is not the main factor leading to the removal of pollutants.The sunlight in the reaction system is beneficial to PC-EB to activate PMS to remove and mineralize pollutants,especially high-intensity sunlight;PC-EB/PMS/sunlight system has good resistance to the interference of anions,especially in wastewater containing high concentrations of chloride ions,APAP can be completely removed within 5 min;PC-EB/PMS/sunlight system mainly relies on electron transfer to oxidize organic pollutants,and the incident light depth of the three-dimensional channel in the PC-EB-900 evaporator can reach 432μm,which is beneficial to improve the reaction interface,realize the shielding,adsorption and oxidation of organic matter and control the VOC residue in distilled water,and the ion concentration of distilled water is much lower than Drinking water standard recommended by the World Health Organization(WHO). |
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