Synthesis of three crystalline phases of Cu₂(OH)₃Cl as Fenton catalysts to mineralize phenol in chloride-free and high chloride solutions

Three crystalline phases of Cu2(OH)3Cl (atacamite, botallackite and paratacamite) were synthesized and used as Fenton catalysts to mineralize phenol in chloride-free and high chloride solutions. Botallackite and paratacamite can be synthesized via a direct precipitation method by tuning the stirring speed or sodium chloride concentration. Fast stirring and high sodium chloride concentration favor the formation of paratacamite. Atacamite can be synthesized by an indirect precipitation method. Three crystalline phases can mineralize >80 % phenol in both chloride-free and chloride solutions. The introduction of chloride further improves their activities. The activities of three crystalline phases follow the order of paratacamite>atacamite>botallackite. The TOC removal of paratacamite respectively reaches 86.0 % and 87.9 % in the chloride-free solution and 15,000 mg & sdot;L- 1 NaCl solution. The catalytic activities are mainly determined by the Cu(+ )percentage of catalysts. The difference in Cu+ percentage of three crystalline phases in Fenton systems is primarily related to the electron transfer between H2O2 and Cu-2(OH)(3)Cl. Paratacamite exhibits the largest Cu+ percentage because it has the shortest Cu-Cl bond and the adjacent layers are linked by chemical bonds, facilitating the electron transfer. Botallackite exhibits the lowest Cu+ percentage, due to the H-bonded adjacent layers. Paratacamite is active and stable in mineralizing organic pollutants in a real saline shale gas fracturing flow-back and production water.