Study On Catalytic Reduction Of Para-chloronitrobenzene With Noble Metal Nanoparticles Aggregation Synthesized By Surfactant-Directed

Chloronitrobenzene compound is a kind of vital raw materials in the chemical industry,mainly used in the production of pesticides,drugs,preservatives,dyes and other products.These compounds are with high toxicity,durability,easy to bioaccumulation and difficult to be biodegradable in natural environment.In addition,the chloronitrobenzene compound is carcinogenic,teratogenic,mutagenic and genetic toxicity to human health.The U.S.Environmental Protection Agency?EPA?,the European Community?EEC?and Chinese State Environmental Protection Agency?SEPA?all have listed chloronitrobenzenes as the priority control pollutant.Hence,it has become an important issue how to effectively remove chloronitro benzenes.In this study,p-chloronitrobenzene?p-CNB?is catalytic reduction and transformed to p-chloroaniline?p-CAN?or aniline with noble metal nanoparticles aggregation catalysts,which also is an important raw material and its toxicity lower than p-chloronitrobenzene.The noble metal nanoparticles aggregations are prepared by chemical reduction method.This research mainly used the electrostatic interaction and self-assembly of surfactant to induce the formation of noble metal nanoparticles aggregati on.Palladium?Pd?,platinum?Pt?and gold?Au?three precious metal were selected as materials to synthesizing nanoparticles,cationic surfactant cetyltrimethylammonium bromide?CTAB?was chose as representative of surfactant and sodium borohydride?NaBH₄?was reductant to reducing precious metal ions to nanoparticles.The results showed that corresponding salt compounds of three precious metal were connected with CTAB because of their electrostatic interaction to each other which can shield the electrostatic repulsion between the hydrophilic groups of CTA⁺.Then it drives the formation of surfactant assemblies on the molecular level which were reduced by NaBH₄,and CTAB-PdNPs,CTAB-PtNPs,CTAB-AuNPs aggregations were synthesized with special regular shapes.This study chose micro-pollutant p-CNB as target pollutant and chose its catalytic reduction and characterized as probe to comparing its structure and catalytic capacity of three nanoparticles aggregation.The results showed that the corresponding noble metal nanoparticles aggregations of Pd,Pt and Au had different structure and physicochemical property caused by itself physicochemical property of three noble metals,which further influence its catalytic properties.P-chloronitrobenzene is catalytic hydrogenation with the three noble metal nanoclusters under the same conditions,CTAB-PdNPs and CTAB-PtNPs can transform all p-CNB into aniline within 120 minutes,while CTAB-AuNPs convert p-CNB into p-chloroaniline and a small amount of aniline within 120 minutes.Therefore,CTAB-PdNPs and CTAB-PtNPs have better catalytic rate and catalytic selectivity.During the cycle experiments,the dechlorination efficiency of CTAB-PdNPs still can achieve 81.9%for the catalytic reduction of p-CNB after eight times,while the dechlorination efficiency of CTAB-PtNPs is only 45.2%after eight times.It means that the catalytic performance of CTAB-PdNPs is more stable than CTAB-PtNPs.Besides,the study further investigated the effect of Pd dosages,CTAB concentration,the initial pH and NaBH4 dosages on the catalytic reduction.The optimum conditions were Pd dosage value of 0.125 mM,CTAB concentration value of 1.0 mM,the initial pH value of 5 and the NaBH₄ dosage value of 15 mM.This research reports a new method of synthesizing noble metal nanoparticles assembly with special regular shapes which could overcome the aggregation of single metal nanocatalysts and synthesize noble metal nanoparticles aggregation with excellent dispersity,stability and catalytic capacity.Besides,it is also studied that the synthetic mechanism of the noble metal nanoparticle aggregation and the catalytic reduction mechanism of p-CNB which provided a feasible technology for catalytic reduction of micro-pollutant p-chloronitrobenzene in the environment.