Preparation Of Solar-driven Lignin Hydrogel-based Evaporator And Its Application For Water Treatment

Water is one of the most important sources of life.Recently clean water shortage is an urgent problem that need to be resolved.Due to the rapid growth of population and the aggravation of environmental pollution,the shortage of fresh water resources has become more serious.Thereby,the recycling of water resources is a global research hotspot.Solar-driven desalination technology has attracted great attention because it's green,sustainable and environment friendly.In recent years,hydrogel has been widely used in the field of solar-driven seawater desalination,but the solar-driven evaporator based on hydrogel still restrained by some problems,such as low evaporation efficiency,high cost and short life time.Therefore,it is urgent to develop a hydrogel-based solar-driven evaporator with high evaporation efficiency,low cost and sustainable operation.Lignin as a kind of biomass waste features with abundant,low cost,environmentally friendly,which could have a good application prospect in the field of water resource recycling.This paper carries out the following research works:(1)We designed and synthesized a lignin hydrogel-based solar driven evaporator for highly efficient seawater desalination.There are some advantages of the designed lignin hydrogel-based evaporator,including facile preparation process and environment-friendly,sustainability and so on.Under the irradiation of 1 solar intensity,the solar-driven evaporator shows a perfect seawater desalination performance.The evaporation rate of water is 1.33 kg·m^-2·h^-1,and the solar steam generation efficiency reaches 75.1%.(2)In order to solve the problem of low evaporation efficiency of lignin-based solar-driven evaporator,we designed a billayer lignin-based hydrogel(polypyrrole/lignin hydrogel)evaporator.Here,a cost-effective lignin-based hydrogel with three dimensional meso/micro-porous structures is prepared by a facile and scalable crosslinking-polymerization strategy.Benefiting from numerous hydrophilic hydroxyls in lignin as well as 3D hierarchical porous structure,the designed hydrogel exhibits sufficient water supplement,effective water activation,as well as fantastic anti-salt accumulation performance.Our lignin hydrogel-based evaporator achieves a high and stable evaporation rate of 2.25 kg·m^-2·h^-1 for 48 h continuous operation without salt crystallizing and blocking,and shows a good stability in a wide range of p H value from1 to 14.In addition,heavy metal ions,including Cu²⁺,Cr O₄^2-,Co²⁺are efficiently removed from polluted water by electrostatic interaction with excess hydroxyl groups in the lignin hydrogel.Therefore,lignin hydrogel-based evaporator offers a cost-effective and long-term anti salt blocking strategy for solar-driven water purification.(3)In order to solve the recovery problem of trace noble metals in wastewater,we further explore the application of polypyrrole/lignin hydrogel in the field of trace noble metals recovery driven by solar pump.Lignin is composed of abundant hydroxyl groups and positive potential under acidic conditions,which can be utilized for selective adsorption of[Au(III)Cl₄]^-The experimental results show that the prepared polypyrrole/lignin hydrogel can selectively adsorb[Au(III)Cl₄]^-at low p H,and the saturated adsorption capacity of Au(III)is reached 505 mg·g^-1.The reducing groups(hydroxyl and aldehyde groups,etc.)contained in lignin can also further reduce Au(III)to Au(0),which can be catch in lignin hydrogel to realize gold recovery.Polypyrrole/lignin hydrogel realizes the treatment of wastewater containing salt and recovery of trace precious metals.