Structure of straw biochar/amino resin doping nanoSiO2 and its phosphorus removal characteristic

Abstract: Phosphorus is one of the key nutrients that cause eutrophication of water bodies, and excessive phosphorus in water will cause water ecosystem structure and function change, deterioration of water quality and landscape, and biodiversity decrease. Therefore, preventive measure of phosphorus pollution in the aquatic environment and processing must be paid more attention. The processing methods of phosphorous water include biological phosphorus removal technology, chemical precipitation, adsorption, and so on. Adsorption technology is efficient and cheap, and has a good removal effect, which has come into notice of researchers. So far, some studies have been conducted on preparation of straw biochar for removal of phosphate radical from aqueous solutions. In this study, a porous nano biochar composite (nanoSiO2/AR-biochar) was prepared by nanoSiO2 doping, which was homogeneously cladded using amino starch resin, and kneading molding, then foaming coking technology were adopted in situ preparation as well as the carbonizing treatment. Transmission electron microscope (TEM), thermogravimetry, scanning electron microscope (SEM), specific surface area analysis, nitrogen adsorption-desorption isothermal and compression were used to characterize the pore structure, thermal stability, microstructure and compression performance of nanoSiO2/AR-biochar. Phosphate adsorption process of nanoSiO2/AR-biochar was studied by means of isothermal and adsorption kinetics. Results showed that the specific surface area, total pore volume, and micropore volume of nanoSiO2/AR-biochars increased monotonously. The nanoSiO2/AR-biochars prepared at 550℃ possessed the maximum single point adsorption total pore volume (0.177 5 cm3/g), and the pore diameter of the ultramicropores was mainly in the range from 1 to 50 nm. The t-plot micropore area, and Brunauer-Emmet-Teller surface area of this kind of nanoSiO2/AR-biochar were 302.86 and 352.70 m2/g, respectively, when the doping amount of nanoSiO2 was 6% of straw powder quality. SEM and TEM analysis showed that the surface of the porous granular biochar materials doped nanoSiO2 could form the similar sponge flocculent structure, which could provide more adsorption sites for removal of phosphate ions. More it was worth mentioning that the compressive strength of nanoSiO2/AR-biochars was increasing from 3.89 to 7.96 MPa, a growth of 104.6%, which could solve the problems such as short service life, difficulty in recycle and dust pollution of traditional biochar. Adsorption experiments showed that the adsorption capacity of the nanoSiO2/AR-biochar could be as high as 18.42 mg/g (within 5 min), higher than straw biochar, of which the process could be described with Ho's pseudo-second-order kinetic model. The result of the adsorption process of phosphate radical conformed to the pseudo-second-order dynamic model, which assumes that the adsorption process conforms to the chemical adsorption. The process after the rapid adsorption accorded with the chemical adsorption assumption, and the initial phase was mainly described by physical adsorption. Compared to the traditional straw biochar material, it has lots of advantages such as high adsorption capacity, high compressive strength, recycling, and environmental friendliness. What was more, according to the design in the work, there would be an excellent market prospect of nanoSiO2/AR-biochar. In a conclusion, the nanoSiO2/AR-biochar has the potential to replace the straw biochar for purifying the polluted water. These results will provide a feasible treatment approach and theoretical foundation to reaserch biochar materials on effectively removing phosphorus from eutrophication waters.