Regulation of free or surface hydroxyl radicals in MILs(Al)-Fe catalyzed Fenton-like systems by free carboxyl group on catalysts.

[Display omitted] • MILs(Al)-Fe with different carboxyl group amounts were used for Fenton-like catalysis. • Surface and free HO are postulated to be the main active species for decontamination. • Free/surface HO formation ratio was positively correlated with carboxyl group amount. • Mechanims of regulation was proposed as steric hindrance and charge density. • Surface HO favored positively charged organic oxidation while free HO did not. Iron based Fenton-like processes have been widely investigated, while how to regulate active species generation still is a problem of concern. In this study, MILs(Al) with various carboxyl group amounts were used as research tools, loading iron for Fenton-like oxidation, to investigate the effect of free carboxyl group on surface or free HO generation. Active species identification indicates that surface and free HO were main active species for carbamazepine removal. Moreover, it was concluded that contribution of free HO for the decontamination was positively correlated with carboxyl group amounts on MILs(Al). With free carboxyl group amounts increasing from 3.07 to 5.09 mmol/g on MILs(Al)-Fe, concentration of free HO for carbamazepine removal increased from 47.4% to 62.5%. The mechanisms of carboxyl group amounts impact the chemical state of HO was proposed as steric hindrance effect and charge density near iron sites. The destruction of carbamazepine was proposed in different systems by intermediates determination, and the results indicate that the existing form of HO mainly influenced the efficiency of pollutant degradation, rather than oxidation mechanisms of it. Various pollutants degradation in different MILs(Al)-Fe catalyzed Fenton-like systems were investigated as well, to understand the superiority of different HO for decontamination. MILs(Al)-Fe with various carboxyl group amounts catalyzed Fenton-like processes could remove 34.2%–73.0% carbamazepine, 56.7%–93.8% sulfamethoxazole, 36.4%–75.6% bisphenol S and 43.8–79.7% salicylic acid. This study understood the regulation of active species by carboxyl group in MILs(Al)-Fe/H 2 O 2 systems, and sheds new light on active species precise regulation in Fenton-like systems. [ABSTRACT FROM AUTHOR]