Microwave hydrothermal-assisted preparation of novel spinel-NiFe 2 O 4 /natural mineral composites as microwave catalysts for degradation of aquatic organic pollutants.

In this study, novel spinel-NiFe2 O4 /natural mineral (sepiolite, diatomite and kaolinite) composites were developed using microwave (MW) hydrothermal method, and applied in MW-induced catalytic degradation (NiFe2 O4 /natural mineral/MW) of organic pollutants such as sodium dodecyl benzene sulfonate (SDBS), azo fuchsine (AF), methyl parathion (MP), and crystal violet (CVL) in solution. Catalytic activities of three NiFe2 O4 /natural mineral composites were compared. The effects of material synthesis process parameters such as molar ratios of NiFe2 O4 and natural mineral, and pH of precursor solutions for synthesizing catalysts, and degradation parameters such as MW irradiation time and catalyst reuse cycles were also investigated. The principle on NiFe2 O4 /natural mineral/MW degradation was provided. The results reveal that organic pollutants in wastewater can be removed completely using NiFe2 O4 /natural mineral/MW within minutes. NiFe2 O4 /sepiolite shows higher catalytic activity than the others. The calculated degradation rate constants are 1.865, 0.672, 0.472, and 0.329 min-1 for SDBS, AF, MP, and CVL, respectively, using NiFe2 O4 /sepiolite/MW system. The performance of NiFe2 O4 /natural mineral can be maintained for three reuse cycles. Active species OH, O2 - , and h+ play main roles in NiFe2 O4 /sepiolite/MW degradation. Hence, NiFe2 O4 /sepiolite/MW technology with rapid and cost-effective degradation, magnetic separation, and no secondary pollution, demonstrates to be promising in treating organic contaminants in wastewater.