Photoelectrocatalysis Degradation Of Persistent Organic Pollutants On TiO₂ Catalyst

Photoelectrocatalysis（PEC）degradation of organic pollutants into CO₂ and H₂O is a promising strategy for addressing ever-growing environmental problems.However,the activity of PEC is substantially limited due to the rapid electron-hole recombination and sluggish surface reaction kinetics for photoelectrocatalyst.Meanwhile,the efficiency of PEC degradation is seriously limited by mass transfer and diffusion of pollutants.Herein,we develop the photoelectrocatalyst system with highly efficient based on titanium dioxide（TiO₂）,and investigate the charge separation,surface reaction kinetics and mass transfer issues in the field of PEC degradation of organic pollutants.The main research results are summarized as follows:（1）We developed a TiO₂ photoelectrode with 3D conical structure,and investigated the influence of catalyst morphology on the degradation of persistent pollutant 4-chlorophenol（4-CP）.The unique conical catalyst can boost the PEC degradation of 4-CP with 99%degradation efficiency and 55%mineralization efficiency.The normalized apparent rate constant of a nanocone catalyst is 5.05h^-1g^-1m²,which is 3 times that of a nanorod catalyst and 6 times that of an aggregated particle catalyst,respectively.Further research reveals that the outstanding activity of nanocone TiO₂ catalyst is attributed to excellent PEC performance of conical morphology.Such conical morphology is facilitated to the efficient charge separation and promoted to the dramatic increase of the amounts of active species.Computational fluid dynamics simulations show that the nanocone structure is beneficial for the mass transfer compared to the other two structures.This result highlights the importance of tuning the morphology of a photoelectrocatalyst at the nanometer scale for obtaining high PEC activity.（2）Based on the understanding to the nanocone TiO₂ catalyst,we introduced cocatalyst nickel oxide（NiO）by photo-deposition method to the nanocone TiO₂catalyst,and investigated the influence of cocatalyst modification on the PEC degradation performance.After loading cocatalyst NiO,the PEC activity of TiO₂ for4-CP degradation at 1.0 V_RHE is increased from 94%degradation efficiency and 30%mineralization efficiency to 99%degradation efficiency and 49%mineralization efficiency.At the same time,the apparent activation energy of surface reaction for TiO₂ decreases dramatically from 17.24 k J/mol to 2.5 k J/mol.Further experiments reveal that the introduction of NiO can not only promote the charge transfer dynamics of TiO₂,but also facilitate the dissociation of water in the surface reaction,which tunes the surface reaction kinetics and reduces the energy barrier significantly.Based on the essential understanding of degradation mechanism,this result highlights the importance of cocatalyst modification for promoting the surface reaction kinetics.（3）Based on the understanding of the mechanism for the catalytic degradation reaction of TiO₂ nanocone system,we designed and constructed a flow catalysis degradation system,and studied the influence of mass transfer on the performance of degradation system.The flow system realizes the forced diffusion of pollutants and improves the mass transfer in the system.After optimization of the flow parameters,the TiO₂ nanocone catalyst achieved 98%degradation and 80%mineralization for4-CP within 6 hours.Compared to the static system,the mineralization performance of the catalyst system is further improved from 70%while the degradation performance is maintained.Moreover,the flow system can achieve 90%degradation and 50%mineralization for other typical pollutants（paracetamol,bisphenol A,hexafluorobisphenol A）,indicating the applicability of the system.This result highlights the importance of mass transfer in degradation reaction,and provides a promising strategy for designing and constructing practical reaction system for PEC pollutant degradation.