| Improving indoor air quality and effectively reducing indoor formaldehyde gas content has become an urgent environmental problem.The utilization of high quality activated carbon from hemp stalk not only reduces the cost of production,improves the subsidiary economic benefit of the hemp,but also is beneficial to the comprehensive utilization of agricultural waste and environmental protection.With the combination of hemp stem based activated carbon and the visible light catalysis material,the indoor formaldehyde gas can be completely degraded into harmless small molecules,which would provide scientific basis for improving indoor air quality in the future.In this study,hemp stalk was employed as raw material to investigate the properties of activated carbon from hemp stalk activated by H3PO4,K2CO3 and KOH activation.The modified titanium dioxide with excellent photocatalytic effect in visible light was prepared by gel sol method,noble metal deposition and semiconductor coupling method.The modified titanium dioxide was loaded on the activated carbon prepared from hemp stalk.The adsorption and degradation of liquid phase and gaseous phase formaldehyde by modified hemp stem based activated carbon were studied.The main conclusions are as follows:(1)Hemp stalk was suitable for the production of super activated carbon quality raw materials.The activated carbon prepared by chemical activation using KOH showed richer pore structure compared to H3PO4 and K2CO3 activation methods.The specific surface area of the prepared hemp based activated carbon was up to 2388 m2/g with rich pores and certain mesoporous pores,and the total pore volume was 1.27 cm’/g,and the average pore size was 2.06 nm when measured with the ratio of activator was 4.5:1(KOH/carbonized material)and activated for 1.5h at 800℃.(2)The doping modification of platinum for titanium dioxide greatly improved the absorption and photocatalytic activity in visible light.The platinum element entered into the TiO2 lattice with Pt4+dominating instead of Ti4+.And also some platinum element existed on the surface of TiO2 in the form of PtO.The prepared photocatalytic material Pt/TiO2/AC with 0.4%of the precious metal platinum doping amount,and 40%(36.63%actually)of the theoretical loading rate of titanium dioxide showed more rapid and efficient adsorption and degradation ability for formaldehyde solution when compared to that of BiVO4/TiO2/AC photocatalyst materials prepared by semiconductor coupling method.(3)The formaldehyde with a concentration of 200 mg/L in 200 mL solution could be removed 98.33%by the prepared composite 0.15 g Pt/TiO2/AC under visible light.The effect of adsorption and,photocatalyst on formaldehyde of the Pt/TiO2/AC composites could be promoted greatly by both acidic and alkaline.The chemical action played a major role in the process of adsorption and degradation of formaldehyde with Pt/TiO2/AC composites,supplemented by physical action.It was a synergistic process of visible photocatalytic degradation and activated carbon adsorption to the removal of formaldehyde.(4)The ratio of adsorption and photocatalytic degradation of 1 m3 formaldehyde gas with a concentration of 40 mg/m3 was up to 96.25%when using 2 g Pt/TiO2/AC composite at the room temperature and the relative humidity of 30%under visible light.Pt was doped in titanium dioxide in the form of PtO and Pt4+ and formed the defect energy level.It acted as photogenerated electrons-photogenerated holes for the formation of center when stimulated by visible light.The produced photogenerated electrons transfered to the guide band of titanium dioxide to stimulate them to be excited,and photogenerated holes migrated to the surface of the catalyst and participated in the photocatalytic reaction.In the process of degradation of formaldehyde by Pt/TiO2/AC under visible light,the free radicals such as photogenerated electrons,photogenerated holes,·O2-and OH have played an important role.Formaldehyde was oxidized firstly to formic acid,HCO3-,and further degraded to CO2 and H2O. |
PDF Full Text Request