Heterogeneous Fenton-like catalytic removal of p-nitrophenol in water using acid-activated fly ash

The use of nitric-acid-activated fly ash (AFA), as heterogeneous Fenton-like catalyst for p-nitrophenol (p-NP) removal from water, was investigated. The physicochemical characteristics of AFA were better than those of raw fly ash (RFA). Under experimental conditions of pH 1.5-5.1, H(2)O(2) dosage 83.3-333 mgL(-1), AFA loaded 5.0-20 gL(-1), and temperature 298-348 K, the p-NP removal rate increased with the increase of H(2)O(2) dosage, AFA loaded and temperature. The highest removal rate (98%) was observed at pH 2.0 when H(2)O(2) dosage 166.5 mgL(-1), AFA loaded 10 gL(-1) and temperature 298 K. However, good p-NP removal efficiency (98.8%) could still be achieved under milder pH (5.1) conditions when enough reaction time (14 h) was applied. The leached iron concentration increased with decrease in pH and with increase in reaction time. The homogenous catalysis caused by leached iron was negligible. The less reaction time and higher AFA load could be selected flexibly for catalytic stability and reusability in actual application. The probable heterogeneous catalytic mechanisms were proposed.