Preparation Of PBAT Porous Monolithic Materials And Its Application In Interfacial Solar Vapor Generation

In recent years,with the development of science and technology and the growth of population,the surge in demand for water resources is accompanied by the aggravation of environmental pollution.The development of traditional seawater desalination and sewage purification technologies was limited because of high energy consumption and high production investment.Solar water evaporation technology has received extensive attention due to its advantages of no energy consumption,cost-efficient,and sustainability.Among them,the interfacial solar vapor generator（ISVG）is considered to be one of the most promising ways to solve the problem of water shortage because of its special structural design,which can achieve high solar energy utilization and evaporation efficiency.However,no matter what kind of ISVG has its service life.In long-term operation under ultraviolet rays,its matrix or light absorber will be damaged and invalid.When the solar evaporator is invalid,how to deal with it so as not to burden the environment is a problem we should consider.Therefore,in this paper,a degradable interfacial solar vapor generator（DISVG）was prepared using PBAT monolith with hierarchical porous morphology as matrix and MXene as the solar absorber.This DISVG achieves efficient seawater desalination and sewage purification with less MXene consumption.And when it is discarded beyond its service life,the matrix can be degraded naturally,without causing pollution to the environment,and realizing harmless treatment.First,Poly（butylene adipate-co-terephthalate）（PBAT）was selected as the raw material,1,4-dioxane as the solvent,and ethanol as the non-solvent.PBAT monoliths with hierarchical porous morphologies were prepared by the non-solvent thermally induced phase separation（NTIPS）method.The microscopic morphology of PBAT monolith was controlled by adjusting process parameters such as polymer concentration,solvent/non-solvent ratio and phase separation temperature.The effect of process parameters on the phase separation and the mechanism was also investigated.The Liquid-Liquid（L-L）phase separation of the PBAT homogeneous solution occurs during the preliminary phase separation process.The homogeneous solution is separated into polymer-rich phase and polymer-poor phase.The polymer phases are connected to form a framework structure,and the polymer-poor phase converges to form pores.A small amount of solvent in the polymer-rich phase forms pores in the framework.After secondary phase separation,it was completely separated into a two-phase structure of polymer phase and solvent phase.The solvent phase was removed by freeze-drying,leaving a PBAT monolith with a hierarchical porous morphology.During the phase separation process,the concentration of the polymer mainly affects the content of the framework of the PBAT monolith,which is reflected in the framework continuity and pore connectivity of the PBAT monolith.The solvent/non-solvent ratio mainly affects the kinetic equilibrium of the system,which affects the degree of phase separation of the solution reflected in the regularity of the pore structure of the sample.The phase separation temperature mainly affects the rate of phase separation,which in turn affects the degree of separation of the solution within the same time.Besides,too low temperature will cause the freezing of solvent phase and hinder the phase separation.The unannealed PBAT monolith has poor mechanical properties and irreversible deformation will occur after compression.We found that the PBAT monolith recovered its proper elasticity after annealing,and the irreversible deformation after compressing80%strain was reduced from 54.12%to 10.82%.The mechanism of the annealing process to improve the mechanical properties of PBAT monolith was analyzed by DSC and SAXS.During the NTIPS process,the phase separation temperature is low,and the crystal structure of PBAT is defective,so the mechanical properties are weak.During the annealing,the crystal structure of PBAT was gradually improved and the thickness of the lamellas was increased,and the mechanical properties were recovered.The mechanical properties and thermal behavior of annealed PBAT monolith at different annealing temperatures and time were analyzed.Considering the energy consumption and keeping the structure of PBAT monolith,it was concluded that annealing at 70°C for 1 h was the best annealing parameter.Using PBAT monolith as the matrix,MXene/PDA@PBAT monolith（MPPM）degradable interfacial solar vapor generator was prepared by in-situ polymerization of PDA and dip-coating of MXene.The resulting sample dip-coated in MXene dispersion at a concentration of 5 mg/m L（MPPM-5）exhibited good light absorption（up to97.07%）in the full solar spectral range from 300 to 2500 nm.The illumination surface temperature of MPPM-5 can reach 79.8°C in air,and it exhibited a high evaporation rate of 1.87 kg·m^-2·h^-1 and high evaporation efficiency of 86.19%during evaporation.Meanwhile,due to its strong hydrophilicity,MPPM-5 exhibits good salt and oil resistance.After the real seawater is desalinated by MPPM-5,the main salt ion concentration in the condensed water is reduced by 3-4 orders of magnitude,which is in line with the drinking water salinity standards of WHO and EPA.In terms of sewage purification,MPPM-5 can realize the purification of oil-in-water emulsion and dye wastewater,and the purification efficiency exceeds 99%.This study provides a sustainable strategy for the design and development of environmentally friendly,efficient,and stable degradable interfacial solar vapor generators.