Enhanced photodegradation of 2,4,6-trichlorophenol over palladium phthalocyaninesulfonate modified organobentonite

This article explores a supported photocatalyst of palladium(II) phthalocyaninesulfonate (PdPcS) onto organoclay for removal of 2,4,6-trichlorophenol (TCP) from water under visible light (lambda > or = 450 nm) irradiation. The composite clay was not only a good sorbent for uptake of TCP from water, but it also exhibited notable activity for TCP oxidation via singlet molecular oxygen, generated in situ from PdPcS photosensitization. Complete dechlorination of TCP could be achieved after TCP was totally oxidized. The initial rate of TCP degradation was observed to increase with the initial amount of TCP sorption, the kinetics following well the Langmuir-Hinshelwood equation. The resulting rate constant of TCP oxidation was found to increase with the alkyl chain length of the intercalated surfactant from dodecyltrimethylammonium to cetyltrimethylammonium and to octadecyltrimethylammonium. Such the trend in photoactivity was in agreement with the catalyst capacity for TCP sorption from aqueous medium. The result showed that enrichment of toxic TCP on the catalyst was indeed an efficient way for enhancement of the photosensitized degradation of target pollutant. However, PdPcS loading led to a notable decrease in TCP sorption, because of partial blocking of the sorptive sites. The optimal loading of PdPcS was about 1.0 wt %. The catalyst was characterized by nitrogen adsorption, X-ray diffraction, visible diffuse reflectance spectroscopy, and TCP sorption, which revealed that the incorporated PdPcS, mainly in the form of photoactive monomer, coexisted with the intercalated surfactant in the bentonite interlayers. Seven repeated experiments demonstrated that the composite clay was relatively stable and could be repeatedly used for sorption and degradation of TCP pollutant via molecular oxygen and visible light.