Preparation And Performance Of Graphene Oxide Modified Geopolymer Membranes

Oily wastewater has caused serious environmental pollution and ecological damage that is difficult to repair,jeopardizing human health and life safety,and has become one of the most serious environmental problems in the world.The superhydrophilic and underwater superoleophobic metal-base mesh membranes have the characteristics of large flux,high separation rate and low energy consumption,and have broad application prospects in the treatment of oily wastewater.However,they have poor separation performance for oil/water emulsions and are ineffective against organic pollutant molecules.Therefore,the challenge of membrane separation technology in wastewater treatment is to develop a multifunctional oil/water separation membrane for the comprehensive treatment of oil-bearing wastewater.In this paper,based on the concept of"treating waste with waste",geopolymer membranes were prepared by granulated blast furnace slag（GBFS）and Fly ash（FA）were used as high-calcium and low-calcium raw materials,respectively.By doping graphene oxide（GO）method to modify geopolymer membranes,using a variety of modern analytical techniques to study the phase composition,microstructure and surface wettability,and explore its water flux,further investigate its application potential in fields such as oil/water separation.The main results were as follows:（1）Graphene oxide modified granulated blast furnace slag-based geopolymer membrane（GO/GBFSGM）was prepared by a“dip-coating”method using high-calcium GBFS and GO as raw materials,NaOH as base activator and a stainless steel mesh as substrate.The results were shown:GO/GBFSGM was rich in hydroxyl groups on its surface,and had superhydrophilic properties and underwater superhydrophobic properties.After adding GO,the samples’hydrophilic and oilophobic properties were improved.The sample with 0.25 wt.%GO content（0.25GO/GBFSGM）had the best hydrophilic properties,and the water flux was as high as 10520.25 kg·m^-2·h^-1,was 26%higher than that of the sample without GO（0GO/GBFSGM）.Under gravity driving conditions,samples with different GO contents showed excellent separation rates（≥98%）for different layered oil/water mixtures（petroleum ether/water,n-hexane/water,kerosene/water and diesel/water）.0.25GO/GBFSGM could effectively separate oil droplets from oil-in-water emulsion.It had good alkali resistance,salt resistance,heat resistance and recycling stability.Adding GO also improved the oil pollution resistance of the sample.（2）Graphene oxide modified fly ash-based geopolymer membrane（GO/FAGM）was prepared by a“dip-coating”method with low-calcium FA and GO as raw materials,NaOH and Na₂Si O₃ as base activators and a stainless steel mesh as substrate.The results were shown:With the increase of GO content,the water flux of the sample showed a trend of increasing first and then decreasing.Among them,the sample with 0.4 wt.%GO content（4GO/FAGM）had the highest water flux(1363 kg·m^-2·h^-1),which was 1.19times higher than that without GO（0GO/FAGM）.GO/FAGM showed that the water contact angle tends to 0°in the air and the oil contact angle was greater than 150°under the water,showed excellent separation rate（≥98%）for different layered oil/water mixtures.4GO/FAGM still showed oil/water separation efficiency greater than 98%in Na Cl solution,NaOH solution,hot water and HCl solution.（3）The adsorption properties of GO/GBFSGM on organic dye molecules were investigated based on the 3D network gel structure of geopolymer.The adsorption rate of0.25GO/GBFSGM for 10 mg·L^-1 methylene blue（MB）solution was more than 91%within 4 h.（4）The photocatalytic degradation of organic dye molecules by GO/FAGM under simulated sunlight was explored.After 120 min photocatalytic reaction,the photocatalytic degradation rate of 4GO/FAGM for MB dye was 99.84%.