Experimental Study On Degradation Of P-nitrophenol By Sodium Borohydride Catalyed By Biochar

P-nitrophenol（p-NP）has strong teratogenic,carcinogenic and mutagenic effects.It is widely used in the fields of medicine,pesticide,dye and wood preservation.While benefiting mankind,it also poses great harm to the ecological environment and human health.In particular,it has high solubility and good stability in water,which is difficult to treat.At present,the liquid-phase hydrogen reduction method using metal based materials as catalysts and sodium borohydride as reducing agent is considered to be one of the most promising methods.However,this method still has the following shortcomings:firstly,it is complex to preparate the metal based catalysts,which is expensive and has the problem of metal secondary pollution;Secondly,the refractory p-nitrophenol convert to p-aminophenol（p-AP）after catalytic reduction,which is easily degradable,but it is not mineralized into non-toxic carbon dioxide and water,and p-aminophenol will still cause environmental pollution.To solve the above problems,biochar（BC）,which is non-metallic,environment-friendly,easy to prepare and low-cost,is used as catalyst in this thesis.The mineralization of p-nitrophenol was realized by two-step reaction.In the first step,biochar catalyzes the reduction of p-nitrophenol by sodium borohydride to produce p-aminophenol;In the second step,under aeration（air）conditions,biochar activates molecular oxygen to mineralize the p-aminophenol generated in the first step.The main research contents and results of this thesis are summarized as follows:（1）The study was conducted to explore the performance,the influencing factors and mechanism of biochar catalyzed reduction of p-nitrophenol by sodium borohydride.The results show that biochar can effectively catalyze sodium borohydride to reduce refractory p-nitrophenol to easily degradable p-aminophenol;The catalytic ability of biochar increases with the increase of preparation temperature,and the biochar prepared at the highest temperature（1000℃）shows the best catalytic activity;At the same time,BC1000showed good stability and recycling performance.After recycling for 5 times,the removal rate of p-NP was still as high as 88.0%.The study of influencing factors shows that the removal rate of p-NP decreases with the increase of the initial concentration of p-NP and the pH of the initial solution,and increases with the increase of the dosage of biochar catalyst and Na BH₄.When the initial pH value is 3.0,the initial concentration of p-NP is20mg/L,the dosage of biochar catalyst is 0.10g/L and the dosage of Na BH₄ is 0.3420g,p-NP can be degraded to p-AP within 30min.The mechanism analysis shows that the conductivity of biochar is the fundamental factor for its catalytic reduction of p-nitrophenol by sodium borohydride.（2）The study was conducted to explore the properties and influencing factors of p-aminophenol produced by oxidative degradation of activated molecular oxygen by biochar.The results showed that biochar could effectively activate molecular oxygen to oxidize and degrade p-aminophenol;When the reaction temperature is 25℃,the dosage of BC1000 is 0.10g/L,the initial pH is 3.0 and the initial p-NP concentration is 20mg/L,the removal rate of p-AP and TOC is 71.9%and 49.7%within 120min.The study of influencing factors shows that the removal rate of p-AP increases with the increase of catalyst dosage;With the increase of aeration rate,it first increases and then decreases;It decreases with the increase of initial concentration and pH of p-AP.