Remediation Of Pentachlorophenol Contaminated Soil Using Surfactants Soil Washing Combined With Graphene TiO₂Photocatalysis

The remediation of chlorinated hydrophobic organic contaminants in soil andgroundwater has become a key global issue. Based on the soil washing photocatalysistechnology, the mechanism of surfactants adsorption procedure as well as its impact onthe partitioning of organic pollutant was developed; effect of soil physico chemicaland mineralogical properties on adsorption of surfactants and pentachlorophenol,photocatalysis of washing solution was researched into; graphene TiO₂catalyst withenhanced photocatalytic performance was synthesized; and the synthesis effect ofcombined surfactant soil washing with TiO₂photocatalytic degradation technics wasanalyzed. Our study solved the key problems in soil washing photocatalysisremediation technology, such as the low efficient surfactants soil washing process fororganic pollutants, the unsatisfying photocatalytic degradation of organic compoundsusing usual TiO₂catalyst, as well as the coupling issue of surfactant soil washing withphotocatalysis procedure.In order to solve the key problem of high surfactant adsorption by soil, and thecomparatively low washing efficiency for HOCs by using single non-ionic surfactant,taking pentachlorophenol （PCP） as the targeted pollutant, we studied the adsorptiondesorption mechanism of mixed surfactants. The addition of anionic surfactant candecrease the adsorption amount of nonionic surfactant by19.332.8%, as well asgreatly enhance the washing efficiency of pentachlorophenol in soil. For thefirst time we used BET, FT IR and thermal analysis to study the adsorptivepattern of mixed surfactants, and its synergistic effect was revealed:（1） theoptimized mixing of surfactants can substantially lower the effective criticalmicellization concentration, so as to decrease the dose of surfactants needed;（2）mixed micelle of high stablity and solubilization ability for PCP would beformed based on the non-ideal mixing effect. With the washing experiments ofreal soils, we discovered that the adsorptive forces for surfactants wereion dipole force and hydrogen bonding, the behavior of pentachlorophenol insoils was mainly dominated by pH value and the organic parts in soil. Using graphene oxide as precursor, the graphene TiO₂catalystsynthesized through hydrothermal method as utilized in the photocatalyticdegradation of chlorinated hydrophobic organic compounds for the first time. Itsdegradation efficiency for PCP Na under UV light achieved97.7–99.0%,about18times higher than P25TiO₂; The photocatalytic degradation pathway ofPCP was mainly dechlorination and the electrophilic addition of OH. ThroughTiO₂photocatalytic degradation of PCP washing solutions, we found that onlythe concentration of TX100and PCP should significantly affect the degradationefficiency.For the first time, we studied the affecting pattern of surfactants onphotocatalysis procedure, which was based on their adsorptive behaviors. In acomplex system, the addition of nonionic surfactant can significantly enhancethe photodegradation efficiency by3.70times, which can be further increasedby2.84times with the addition of anionic surfactant. Through the experimentsof real soil, we proved that surfactant soil washing coupled with graphene TiO₂photocatalytic degradation technology can successfully realize the remediationof pentachlorophenol contaminated soil.