Abstract:

Objective The pollution of dye wastewater to the environment is the main factor restricting the large-scale production of the textile industry. Sodium alginate (SA) and graphene oxide (GO) both have good adsorption on residual dyes in dye wastewater. This paper reports a research that combines sodium alginate and graphene oxide are for fiber spinning, and studies the adsorption of dye wastewater of the composite fiber for the optimal absorption effect and recovery of adsorbent materials.
Method In this research, graphene oxide was used as an additive, sodium alginate was used as the main material of the gel, where graphene oxide was grafted with maleic anhydride for modification. SA/MAH-GO (modified graphene oxide) composite adsorbent material was prepared by wet spinning, microscopic pore-forming, freeze-drying, and so on. Fourier infrared spectrometer, differential scanning calorimeter, scanning electron microscope, X-ray diffractometer, particle size analyzer and other instruments were used to test and characterize the product. Additionally, an ultraviolet spectrophotometer and a fiber tensile breaking strength meter were used to compare its adsorption properties and physical and mechanical properties.
Results At the microscopic level, the chemical structure and particle size of GO have changed after grafting with maleic anhydride. FT-IR test showed that the infrared spectrum of MAH-GO particles illustrated an ester base vibration peak at 1 101 cm^-1, which proved that maleic anhydride was successfully grafted onto the GO surface lamellar (as shown in Fig. 1). After ultrasonic dispersion, the particle size of MAH-GO in the water medium is mainly distributed within 191.2 nm, much smaller than GO particle size (9 669.8 nm), and the dispersion of MAH-GO is obviously better than GO particle. The experimental results show that trace amounts of modified graphene oxide (MAH-GO) have a certain optimization effect on the physical and mechanical properties of SA/MAH-GO microporous aerogel fibers. On the other hand, the special structure of microporous aerogel fibers has improved its adsorption capacity of methylene blue dyes. When the mass fraction of MAH-GO is 0.5%, the maximum tensile breaking strength is 0.513 cN/dtex, the breaking strength is increased by 11.51% compared with unmodified GO, and the breaking strength is increased by 81.27% compared with the microporous SA aerogel fiber (as shown in Fig. 4). Microporous aerogel fibers containing 0.75% MAH-GO demonstrated a higher removal rate of methylene blue, and the removal rate is always above 80% in the mass concentration range of 200 mg/L to 1 800 mg/L, and the maximum adsorption capacity can reach 2 400.6 mg/g (as shown in Fig. 6 and 7).The fitting results of the quasi-secondary kinetic adsorption model and the Langmuir isotherm adsorption model prove that the adsorption process involves electron sharing or transfer between the adsorbent and the adsorbate.
Conclusion Composite adsorption materials have good development prospects for adsorption of polluted wastewater. The raw materials such as calcium carbonate particles and sodium alginate used in the preparation of micro-porous adsorption fiber are cheap. When the mass fraction of MAH-GO is controlled within 0.75%, the cost actual treatment of low concentration methylene blue pollutants can be further controlled. To sum up, there are some suggestions for the next research of this topic. Firstly, the organic solvent DMF is used in the esterification process of graphene oxide, which can be recycled by vacuum distillation, but it is time-consuming and energy-consuming. Environmental friendly solvents and modified catalytic methods such as ultraviolet photocatalysis should be selected. Secondly, besides the pore-forming method, mineral materials such as bentonite, montmorillonite and diatomite can also expose more potential adsorption sites for sodium alginate composites and improve the adsorption potential of composites for cations, which deserves further exploration.

Key words: modified graphene oxide, light calcium carbonate, sodium alginate, aerogel, adsorption performance, cationic dye