Preparation Of Wood-based Photothermal Conversion Materials And Their Seawater Desalination Performance

Wood was one of the most abundant rencwable resources on the earth.Because of its high mechanical strength,good processability and biodegradability,it was widely used in all aspects of human life,including construction,textiles,and new materials,etc.Among them,basswood was a kind of excellent wood.Its pipe holes were uniform and the flux was high.There were very few intrusive bodies blocking the pipe holes.The pipes had thickened threads and good support performance.After surface carbonization,it had a good performance in the field of photothermal materials and seawater desalination.In this study,the basswood block,that was the original wood,was used as the raw material.The wood-based photothermal conversion material was obtained through uniform hydrothermal carbonization treatment,and it had excellent seawater desalination performance.The work was carried out as follows:A reactor was used to hydrothermally carbonize the original basswood blocks in deionized water.This method uniformly carbonized the wood,with little cracking and deformation,and obtained a uniform carbonized wood(UCW).Five kinds of samples were obtained by controlling different temperatures and time,and sample with better performance(UCW5)and better reaction condition(180?,8 h)were selected according to the photothermal conversion performance test.Using scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy(XPS)characterization methods,the micromorphology of the control sample and UCW5 and the distribution of C and O elements were analyzed.The results showed that UCW5 retained the basic morphology and structure of the wood,but part of the pore diameter shrinked slightly.UV-Vis-NIR spectrophotometer(UV-Vis-NIR),contact angle and thermogravimetric(TG)analysis showed that compared with the control sample,UCW5's light absorption performance,hydrophilic performance and thermal stability performance had been significantly improved,indicating that UCW5 was a better water evaporation material.However,the above hydrothermal carbonization condition was mild,the carbonization was not sufficient,and the photothermal conversion capacity needed to be improved.To this end,the catalyst p-toluenesulfonic acid(p-TsOH)was introduced to treat the basswood by catalytic hydrothermal carbonization.At the same time,delignification treatment was performed to obtain a fully carbonized wood with reduced lumens(R-CW).Five samples were obtained by controlling different temperatures and the concentrations of p-TsOH solution.The water evaporation performance test showed that R-CW5 had the better performance.The micromorphology and elemental characterization and analysis of R-CW5 by SEM,XPS and X-ray diffraction(XRD)showed that the catalytic hydrothermal carbonization and lignin removal of p-TsOH reconstructed the internal morphology of the wood and made most of the pore diameter shrink.The small diameter of the cavity enhanced the capillary force and was more conducive to the transportation of water.p-TsOH not only removed the hydrophobic lignin,but also introduced more hydrophilic functional groups,which significantly improved the hydrophilicity.The analysis of R-CW5's photothermal performance,thermal conductivity,stability and bacteriostatic performance,hydrophilicity and water transport capacity showd that R-CW5 had excellent light absorption performance,good photothermal conversion performance and efficient water transport capacity.At the same time,R-CW5 also had lower thermal conductivity,better thermal stability and bacteriostasis and stronger hydrophilicity than the original basswood block,which showd that R-CW5 was suitable for seawater desalination material.The analysis of seawater evaporation rate of R-CW5 under different light intensity showed that R-CW5 had excellent seawater evaporation performance.Inductively coupled plasma spectroscopy(ICP)was used to characterized and analyzed the concentration changes of the four main ions(Na+,K+,Ca2+,and Mg2+)before and after seawater evaporation to prove that the concentration was significantly reduced below the international drinking water ion concentration standard.The enthalpy of water evaporation of R-CW5 was reduced by the evaporation of water clusters and the shrinkage of the evaporation channel,and the enthalpy of water evaporation of R-CW5 was calculated by differential scanning calorimeter(DSC)analysis.The desalination stability of R-CW5 was good.After 50 cycles of evaporating sample under one sun,the evaporation efficiency of R-CW5 in seawater was stable at about 88%.