Investigation Of Abiotic Reduction Ability Of Oxidized Hydrothermal Biochar Prepared By Low Temperature Oxidation Under Air

Hydrothermal carbonization is considered to be an environmentally friendlytechnology because of its short reaction cycle, high efficiency, less secondary pollutionand no requirement of pretreatment before reaction. The products of hydrothermalcarbonization (hydrochar) have been widely used in catalysis, soil amelioration, waterpurification, energy storage, carbon sequestration, and so on. However, exsiting reportsassociated with the reducing ability of hydrochar are extremely rare.In this paper, Spartina alterniflora was used as the raw biomass for hydrocharand oxidized hydrochar prepartion. The optimum preparation parameters of oxidizedhydrochar were investigated (including hydrothermal temperature, time and lowtemperature treatment time, temperature). Reduction of Fe(Ⅲ) ions by severalmaterials (Spartina alterniflora biomass, Hydrochar and oxidized hydrochar) weretested to know the effect and mechanism. In addition, these materials were tested forthe removal of methylene blue (MB) by adsorption and fenton-like reaction. Thecomposition, structures and morphology of the original biomass, hydrochar, andoxidized hydrochar were characterized by BET, infrared spectroscopy, scanningelectron microscopy, elements analysis, X-ray photoelectron spectroscopy and Boehmtitration. The following conclusions can be drawn from current research:The optimum condition for activated hydrochar preparation is hydrothermalcarbonization at240oC for4h and low temperature heat treatment at240oC for10min. Under this condition, the yield of activated hydrochar is12.91%and H/C andO/C are0.67,4.51repectively. Low temperature heat treatment increased the surfacearea, pore size and the number of oxygen containing functional groups of samples,which improved the Fe(Ⅲ) reducing capacity and adsorption capacity of methyleneblue.Oxidized hydrochar can achieve a Fe(Ⅲ) reducing capacity of120.46mg/g at aintitial Fe(III) concentration of200mg/L, an intial pH of2.0and sample dosage of1g/L. In addition, the reducing ability of oxidized hydrochar can last for6runs of reaction, but show reduced capacity with the increasing of cycle time. After exhuased,the reducing ability of samples can be easily restore (93.90%of initial value) viafurther low temperature oxidization at240oC for10min. By FTIR, XPS and boehmtitration tests, the contents of oxygen containing functional groups (mainly carboxyland carbonyl group) on the surface were found to sharply increase after oxidizationpretreatment. Combined with reduction experiment data, the carboxyl and carbonylgroup is considered to be the primary functional groups responsible for Fe(Ⅲ)reduction.Oxidized hydrochar can adsorp96.1mg/g MB at an intial MB concentration of200mg/L, pH of4.0and dosage of2g/L with final equilibrium time over72h.Because of excellent reducing ability to Fe(III) achieved by oxidized hydrochar, aFenton-like reaction by using oxidized hydrochar instead of Fe(Ⅱ) is proposed andtest for MB decoloration. The results show that oxidized hydrochar can remvoe99.21%of MB within3h at the present of H2O2, which is significantly higher than H2O2absent control test. MB remvoval by oxidized hydrochar and H2O2is considered to bethe synergy of adsorption and degradation, and·OH triggered by the reaction ofoxygen contained functional groups and H2O2is supposed to be responsebile for MBdegradation.