Ultrasound-assisted Preparation Of NZVI-Pd/PAC And Treatment Of CR And MB In Water

Dyeing wastewater has the characteristics of high chroma,high COD,a large amount of water,complex composition and difficulty to degrade.Methods utilizing the physical and chemical processes have a short life,high cost and difficulty sorbent regeneration characteristics.The method of using microorganism treatment also has many uncertain factors,such as poor biodegradability,long cycle and poor stability.Therefore,it is essential to find efficient and stable materials to treat dyeing wastewater.In recent years,Nanoscale Zero-valent Iron(nZVI),a material that can quickly and deeply treat printing and dyeing wastewater,has attracted extensive attention and research from scholars.However,due to the defects of easy agglomeration,poor stability and easy oxidation in the air,nZVI reduced the degradation activity.To address these issues,the electrodeposition method was used as the theoretical basis in the experiment.The ultrasonic-assisted electrodeposition method was used to prepare the supported nano zero-valent iron-palladium/powder activated carbon(nZVI-Pd/PAC).The orthogonal test method was used to optimize the parameters of the preparation process to determine the optimal preparation conditions,and the dye removal test was conducted on behalf of Congo red(CR)and methylene blue(MB).The nZVI-Pd/PAC was characterized by Scanning electron microscope(SEM),energy spectrometer(EDS),X-ray diffractometer(XRD),X-ray photoelectron spectroscopy(XPS),specific surface area,porosity analyzer(BET)and other instruments.Analysis of test results shows the prepared nZVI-Pd/PAC nanomaterial contains zero-valent iron and zero-valent palladium,and the particle size is uniform,the particle size is about 50 nm,and has better catalyst potential.The effects of nZVI-Pd/PAC on the removal rate of dyes Congo red(CR)and methylene blue(MB)were investigated under different influencing factors.The experimental results displayed that the removal rate of MB by nZVI-Pd/PAC is higher than that of CR.After 3 hours of reaction,a higher CR dye removal efficiency of 78.97%was obtained with the optimal parameters initial p H at 6.0,dye concentration at 30 mg L-1,reaction temperature at 50?respectively;A higher MB dye removal efficiency of98.48%was obtained with the optimal parameters initial p H at 5.0,dye concentration at30 mg L-1,reaction temperature at 50?respectively.A small amount of Cl~-can increase the degradation efficiency of nZVI-Pd/PAC for CR,but its removal rate decreased slightly,and the presence of Cl~-hinders the degradation of MB by nZVI-Pd/PAC.The presence of sodium carboxymethyl cellulose(CMC-Na)and sodium dodecyl benzene sulfonate(SDBS)can separately inhibit the degradation of CR and MB by nZVI-Pd/PAC.Finally,the removal effect of CR,PAC,nZVI-PAC and nZVI-Pd/PAC on CR was studied.The results show that the introduction of metal palladium in nZVI-PAC can significantly improve the degradation reaction activity of Fe~0.The kinetics study of CR removal reaction shows that the reduction of CR by nZVI-Pd/PAC follows the law of Langmuir-Hinshelwood first-order reaction kinetics.Besides,nZVI-Pd/PAC nanomaterials have incomplete continuous removal of CR and MB.The re-deposition and regeneration effect of nZVI-Pd/PAC is good.After five regeneration reactions,the MB removal rate of nZVI-Pd/PAC prepared can still reach84.44%.To study the mechanism of catalytic reduction reaction of nZVI-Pd/PAC,analysis by ultraviolet-visible spectrophotometer(UV-Vis)and gas chromatography mass spectrometry(GCMS),the degradation intermediates of CR are biphenyl,Benzidine,and other substances;the metabolite of MB is N,N-Dimethylaniline and 2-amino-5-dimethylamino-benzenesulfonic acid.The degradation mechanism is surface adsorption,reduction of zero-valent iron,and palladium catalyzed.