Study On Molybdenum-Based Materials As Cocatalysts In Fenton-Like Reaction For Typical PPCPs Degradation

Pharmaceutical and Personal Care Products（PPCPs）are found in a variety of water bodies as an emerging class of pollutants.As organic pollutants,they are difficult to degrade effectively by conventional biological methods.Fenton-like systems with persulfate（PDS）as the oxidant can generate sulfate radicals（SO₄·^-）with better oxidation ability,but the slow reduction and rapid precipitation of Fe³⁺severely limit the formation of reactive oxygen species（ROS）.In order to solve these problems,Mo-based co-catalysts（Mo powder,α-molybdenum carbide（α-Mo C）andβ-molybdenum carbide（β-Mo₂C））are used to form a co-catalytic Fenton-like system in this paper.Mo-based co-catalysts possess multiple valence states（0,+3,+4,+5 and+6）providing multiple reduction active sites,promoting Fe²⁺/Fe³⁺cycling and inhibiting the production of ferrous sludge.Details of this study are given below.The details of the study are as follows.（1）Mo was used as a co-catalyst to construct the Fe³⁺/PDS/Mo system for the degradation of sulfamethoxazole（SMX）.SMX was efficiently eliminated（96.7%）after 20min under the circumstances of 0.07 g·L^-1 Fe³⁺,0.50 g·L^-1 PDS,0.20 g·L^-1 Mo,and beginning p H 5.4.SO₄·^-was confirmed as the main reactive oxygen species（ROS）by free radical identification experiments.Based on the valence characterization of Mo before and after cycling,it was deduced that Mo⁴⁺and Mo⁰ facilitated the Fe³⁺/Fe²⁺cycle.A series of material characterizations validated the good cyclic stability of Mo before and after the reaction.Product analysis was adopted to determine the byproducts of SMX and its toxicity was assessed by T.E.S.T software.In particular,Mo was immobilized on cyanoacrylate and agar by a simple mixing and molding step to convert the 2D Mo powder into a 3D bulk Mo-based material.This research affords a promising inorganic Fenton-like system for water treatment.（2）α-Mo C was applied as a co-catalyst for the first time to remove metronidazole（MTZ）by composing an Fe³⁺/PDS/α-Mo system.Under the optimal reaction conditions,29.1μM MTZ was degraded 87.5%in 15 min.Free radical identification experiments show that the key ROS is SO₄·^-.Probe experiments and calculations showed that the contributions of SO₄·^-,hydroxyl radicals（?OH）and non-radical pathways to MTZ oxidation were 58.68%,22.23%and 19.09%,respectively.The good cycling stability ofα-Mo C was verified based on cycling experiments and characterization.The valence characterization and electrochemical test results demonstrate that The valence characterization and electrochemical test results demonstrate that Fe³⁺reduction and Fe²⁺regeneration between Mo and Fe are achieved through electron transfer.（3）β-Mo₂C was utilized for the first time as a co-catalyst to degrade dexamethasone（DXM）by forming an Fe³⁺/PDS/β-Mo₂C system.This system can remove more than 90%DXM in the wide p H range（3.4 to 9.4）.The combination of three radical identification methods comprehensively confirmed a series of reactive species(?OH,SO₄?^-,superoxide radicals（O₂?^-）,singlet oxygen（¹O₂）,and high-valent iron(Fe（IV）were formed during the process,with SO₄?^-playing a dominant role.The circulation of Fe³⁺/Fe²⁺was driven through the exposed sites of Mo²⁺/Mo⁴⁺on theβ-Mo₂C,facilitating the activation of PDS.Various characterization and density flooding theory calculations reveal that adsorption between Fe³⁺andβ-Mo₂C can form Mo-Fe bonds and prolong Fe-O,improving electron transport fromβ-Mo₂C to Fe³⁺and the reduction of Fe³⁺.