Removal Of Organic Pollutants In Water With Biochar-composites

Different types of recalcitrant organic pollutants are often found in wastewater,which could cause serious harm to human health and ecological environment.Therefore,it was necessary to develop adsorbents and catalysts which could efficiently remove organic pollutants in water to purify the water environment.Biochar could be prepared from a wide range of organic materials,which demonstrates promising application in sorption and degradation of organic pollutants.In this paper,biochar(BC)was used as a support matrix for various catalysts such as zerovalent iron(ZVI),elemental silver(Ag0),and Ag3PO4/?-Fe2O3 heterojunctions.The BC-based composites were characterized and tested for removal capacity and associated mechanisms of tetracycline(TC),methylene blue(MB),Rhodamine B(RhB)and ciprofloxacin(CIP).The main results of this paper are as follows:(1)BC supported ZVI(BC/ZVI)was prepared by one-step co-pyrolysis of hematite and pine in nitrogen environment.The results showed that the BC/ZVI composites were prepared by co-pyrolysis of hematite and pinewood.Hematite was completely converted to ZVI in the presence of pine,whereas transformed to Fe3O4 FeO or ZVI without pine.At pH 5,the removal capacity of TC by BC,ZVI and BC/ZVI was 8.02,177.70,and 301.39 g kg-1 BC/ZVI,respectively.The removal mechanism of TC by BC/ZVI included surface adsorption via iron complexation and catalytic degradation.Therefore,agricultural and industrial wastes can be recycled through one-step co-pyrolysis to efficiently remove TC from wastewater.(2)Pinewood BC(PBC)-supported metallic silver(Ago)was prepared via a one-step carbothermal reduction route(AgH)or a wet-chemistry reduction method(AgW).XRD and SEM confirmed Ago was soldered on PBC.Low MB sorption was observed for unsupported Ago nanoparticles(AgNP),AgH and AgW.Under ultraviolet(UV)light irradiation,net MB degradation by AgH(15.88 g kg-1)was higher than that of AgW(12.50 g kg-1)and AgNP(10.27 g kg-1).Total organic carbon(TOC)content after reaction corresponded closely to reduction of MB in solution.Electron paramagnetic resonance(EPR)revealed that MB was degraded by reactive free radicals(ROS)such as hydroxyl radical(·OH),superoxide radical(O2·-)and singlet oxygen(1O2).The scavenging experiments further suggested that ·OH scavengers suppressed MB degradation to a greater extent than other quenchers.Compared to AgW,AgH possessed greater abundance of persistent free radicals,which enhance ROS generation.PBC could also improve separation of electron-hole(e--h+)pairs and enhance electron transfer ascribing to favorable carbon structure.Besides,PBC-Ago maintained good antimicrobial efficacy over E.coli DH5?.A simple photocatalyst prepared by carbothermic method can be used to remove organic pollutants and inhibit microorganisms in water.(3)A graphitic carbon(BC)harbored Ag3PO4/?-Fe2O3 type-I heterojunction(Ag-Fe-BC)was prepared by a hydrothermal-impregnation method to improve electron transfer ability of heterojunction.The photoelectrochemical tests demonstrated that BC enhanced the light adsorption of the heterojunction and promoted the separation and migration of electron-hole pairs.The photocatalytic activity showed the Ag-Fe-BC could degrade Rhodamine B(RhB)by up to 92.7%,i.e.,2.27 and 34.26 times higher than Ag3PO4 and ?-Fe2O3,under visible light.Electron paramagnetic resonance and scavenging experiments confirmed the major reactive oxygen species(ROS)consisted of singlet oxygen(1O2)and superoxide(·O2-).Excellent RhB adsorptive capacity and electrical conductivity of BC facilitated electron-hole separation and then electron transfer to target organics(RhB,TC and CIP)followed by elevated degradation.Thus,a simple method had been used to successfully synthesize photocatalysts with a wide range of pH adaptation and could respond to visible light for the degradation of various organic compounds in water...