Adsorptive Removal Of Tetracycline And Methylene Blue By Activated Carbon Prepared By Nano-copper Catalyzing In Activation Process

In sight of the advantages of nano materials and the catalytic influence of transition metals on pyrolysis of organic compounds, the connection of porous activated carbon preparation and nano-metal technology is considered to be a promising field of research which needs to be explored further. The present study explores the possibilities of employing copper nanoparticles (nano-copper) as catalyst and copper(II) chloride as doping agent in the activation process to prepare activated carbons from platanus orientalis leaves by H3PO4 activation.Two kinds of heating methods were used:conventional heating method and microwave rapid heating method. The three kinds of conventional heating activated carbons by original H3PO4 activation, nano-copper catalytic activation and Cu(II) doping activation were identified as CHAC, CHAC-Cu, and CHAC-Cu(II), the three kinds of microwave heating activated carbons were identified as AC, AC-Cu and AC-Cu(II), respectively. Characterization of these activated carbons as well as adsorption experiments using tetracycline (TC) and methylene blue (MB) as target contaminants were conducted, the main research contents and conclusions are summarized as follows:(1) These carbons were characterized by thermogravimetric analyses (TGA), scanning electron microscopy (SEM), BET surface area analysis and Fourier transform infrared spectroscopy (FTIR). The effects of nano-copper and copper(II) chloride on the activation of these carbons were compared and discussed. Thermal analysis results illustrated that introduction of nano-copper and copper(II) chloride into the activation process accelerated the decomposition of precursor. The surface areas of CHAC, CHAC-Cu and CHAC-Cu(II) were 816.751,836.539 and 831.674m2/g, while AC, AC-Cu and AC-Cu(II) were 1043.967,822.627 and 1118.900 m2/g, respectively. All of the six kinds of carbons exhibited relatively high pore volume compared to those activated carbons with similar surface areas. AC-Cu possessed more surface functional groups than the other samples, and the microwave heating carbons have more functional groups than conventional heating ones in general.(2) The tetracycline adsorption onto CHAC, CHAC-Cu, CHAC-Cu(H) was studied. It was found that the TC adsorption was influenced by solution pH and the maximum adsorption amounts of the three carbons were all reached at pH=7. The adsorption kinetics study revealed the TC adsorption onto the three carbons agreed well with pseudo-second-order model. The adsorption isotherms study suggested the TC adsorption was preferential adsorption, the adsorption capacities of CHAC, CHAC-Cu, CHAC-Cu(II) were 856.4,1388.05 and 1190.78mg/g, respectively. The introduction of nano-copper and Cu(II) not only changed the adsorption mechanism from monolayer adsorption to multilayer adsorption, but also increased the surface active sites and functional groups, leading to the great growth of adsorption capacities.(3) The methylene blue adsorption onto AC, AC-Cu AC-Cu(Ⅱ) was also studied. MB adsorption by AC firstly decreased then increased with the increase of solution ionic strength and agreed well with Langmuir isotherm model. MB adsorption by AC-Cu and AC-Cu(II) were almost independent with the ionic strength and followed the Freundlich isotherm best. The three kinds of carbons presented high methylene blue adsorption capacities of 596.08 、744.11 and 677.48mg/g, respectively.(4) The mechanism of nano-copper catalysis consists of the following aspects:(a) nano-copper particles have huge surface area and will adsorb gaseous products generated in the decomposition process; (b) the copper atoms located in the defect sites are in a condition of electronic unsaturated and exhibit intense tendency of electron acceptance, making it easily that these part of copper atoms combine with polysaccharides and other organic compounds to form complex, which accordingly lower the activation energy and accelerate the pyrolyzation of precursor; (c) due to the superior diathermancy of metallic element, the junction sites of copper particles and carbon precursor would become locallized hot spots, which are beneficial for the thermal conduction and decomposition processes; (d) the scraping and embedding of the rigid nano-copper granules into the carbon precursor which were beneficial to the activator entry and activation accomplishment; (e) the introduction of nano-copper increases the active sites and surface functional groups of activated carbons which are ganerated in the activating process and can react with the decomposition products, therefore naturally promoted the decomposition reaction.