Synthesis Of Zirconia-core Ceria-shell Composites And Its Photocatalytic Performance To Phenol

Currently, environmental pollution has become a major global issue and the water pollution problem is particularly urgent. Sewage contains numbers of organic compounds which are hardly degraded. As one of representative organic pollutants, phenol exerts great harm to both humans and entironment. In the numerous sewage-treatment technologies, photocatalytic degradation of organics is considered to be one of the most promising technologies.As one of the maximum reserves and the most widely studied rare earth oxides, CeO₂ is widely used in light, polishing, electronic ceramics, water pollution and other fields. Wherein, in the field of photocatalytic degradation, compared with Ti O2, CeO₂ photocatalyst has been paid more and more attention because of its lower band gap and higher redox activity. In recent years, with the exploitation and exportation of rare earth being restrained, the international price shows an increasing trend. How to efficiently use expensive rare earth resources has drawn great attentions of relevant countries and scholars. ZrO₂ is a cheap, readily available and inclined to generate oxygen vacancies inorganics. ZrO₂ nanoparticles possesses high specific surface area and rich surface defects, when being used as catalyst carrier, it may exert strong interactions with the catalyst to heighten the catalytic performance. Combined the characteristics of CeO₂ and ZrO₂, in this paper, we designed a photocatalyst of CeO₂@ZrO₂ core-shell structure composites and to be used for photocatalytic degradation of phenol solution.Preparation of ZrO₂ particles: well dispersed cubic crystal ZrO₂ nanoparticles with 30-50 nm size were prepared via hydrothermal method. Experimental results indicated that, under the conditions of C?Zr4+?=0.2 mol·L-1, 60 min precipitant feeding time, hydrothermal temperature and time were 180 ? and 12 h respectively, we could get ZrO₂ particles with high crystallinity, uniform and good dispersion state.Preparation of CeO₂@ZrO₂ core-shell structure composites: In the subsequent coating process, CeO₂ formed shell on the surface of ZrO₂ cores via the method of in-situ chemical precipitation. By investigating the coating effect of the ratio of CeO₂ and ZrO₂, Ce3+ concentration, precipitant feeding time and surfactant, we could prepare well coated CeO₂@ZrO₂ core-shell structure composites under the conditions of ZrO₂ with Na OH for p H modification, 60% ratio of CeO₂ and ZrO₂, C?Ce3+? = 0.03 mol·L-1, and 120 min of the precipitant feeding time. The contrast experiment was executed to differentiate substantially the contribution to generating core-shell structure of heterogeneous nucleation and electrostatic adsorption. The results showed that heterogeneous nucleation's contribution to core-shell structure accounted for 30%.Photocatalytic degradation of phenol: CeO₂@ZrO₂ core-shell composites were applied to the photocatalytic degradation of phenol solution, the results showed that, after 3h photocatalytic reaction, 60% CeO₂ coating ratio of CeO₂@ZrO₂ core-shell composites in photocatalytic degradation of the concentration of 10 mg·L-1 phenol solution, phenol degradation rate could reach 61.27%. Compared with pure CeO₂, photocatalytic efficiency of per unit mass CeO₂, 60% CeO₂ coating ratio of CeO₂@ZrO₂ composites is 2.15 times that of the pure CeO₂ under the same photocatalytic conditions. In the study of photocatalytic reaction conditions, it was found that the catalyst dosage, the initial concentration of phenol and the p H value of the solution would also affect the degradation rate of phenol. Better performance of phenol degradation was obtained by the catalyst concentration was 200 mg·L-1 in 10 mg·L-1 phenol solution. Initial phenol concentration has great influence on the ultimate degradation rate of phenol, for example, when the initial phenol concentration is 5 mg·L-1, after 3 h photocatalytic reaction, phenol degradation rate reached 57.54%, but when the initial phenol concentration rose to 20 mg·L-1 and 40 mg·L-1, phenol degradation rate fell to 49.26% and 32.24% respectively. The p H of photocatalytic reaction mainly reflected that acid reaction condition would promote to generate more active factors, such as ·OH and ·HO2 which could markedly increase degradation rate of phenol. While alkaline reaction condition would inhibit the generation of ·OH in some degree and exert negative influence to photocatalytic degradation of phenol.