Novel Rice Husk Composites:Preparation And Their Applications In Adsorption,Catalytic Degradation,and Microwave Absorption

Rice husk,a byproduct of rice,is treated as an abundantly agricultural waste.The most common disposal of rice husk is burning at open field,generating environmental pollution and resource wasting.Rice husk can be considered as cheap and renewable source of silica,cellulose and lignin with stable supply.Therefore,it is extremely important to develop the technologies for the processing of rice husk into high-value added materials and promote the comprehensive utilization of rice husk.Microwave induced tecnology has gained growing attention of scientific research and various applications due to its adavantages of high efficient,easy operation,high degree of mineralization and energy saving.In this study,we firstly investigated the potentiality of rice husk using as low-cost absorber for dyeing wastewater treatment.Secondly,rice husk based materials were prepared for the investigation of their eletramagnetic absorbing property.Then,we synthesised rice husk/ferrit nanocomposites and studied its detailed catalytic degradation behavior of combining with microwave-induced technology for methylene blue(MB)treatment.In addition,microwave enhanced Fenton process to remove MB from aqueous solution was investigated.The main conclusion were summerized as follows:(1)The prepared RHA with a bulk density of 0.4 g cm-3 is mainly composed of carbon and silica(Chapter II).The absoption of RHA for eletramagnectic waves(EM)was mainly achieved by dielectric loss.Sufficient conductive carbon and the formation of conductive networks are prerequisites for reasonable complex permittiviy values,thus RHA which was ashed at the temperature above 700 ? exhibited better EM abosrbing property.The calculated EM wave absorption of RHA achieved a maximum reflection loss(RL)of-21 dB at 2 to 19 GHz,including 5 GHz with an RL<-10 dB.With advantages of high EM wave absorption,low density and low cost,RHA is a promising light-weight EM wave absorber.(2)In this section,we carried out the magnesiothermic reduced the rice husk ash under differnent temperature and investigated the electromagnetic wave adsorption of products(Chapter III).The EM absorbing for all samples are mainly depend on the dielectric loss,which is ascribed to the carbon and silicon carbide content.Therefore,samples which were magesiothermic reduced from BRHA display considerable higher dielectric loss values and broader bandwidth for RL<-5 dB and-10 dB.The maximum bandwidth for-5 dB and-10 dB decrease with carbon contents,while the optimum thickness decreases with SiC content.The optimum thickness of samples for EM absorption is 1.5-2.0 mm,with maximum RL of between-28.9 and-68.4 dB,bandwidth of 6.7-13.0 GHz for RL<-5 dB and 3.2-6.2 GHz for RL<-10 dB.(3)Rice husk ash is an effective and low-cost adsorbent for water purification(Chapter IV).Chemical composition and morphology characteristic of prepared rice husk ash were mainly affected by the calcination atmosphere and temperature.RHA ashed in nitrogen(BRHA)exhibit higher BET surface,microscope volume,and substianal carbon content,while WRHA(ashed in air)have higher mesopore fraction and silica content.The adsorption capacity of RHA for MB is mainly determined by mesopore volume due to the size of MB molecules.The adsorption kinetics of MB adsorption by RHA fit pseudo-secondorder model.The maximum adsorption capacity q0 is 50.51 mg g"1.The adsorption isotherms fit the Langmuir isotherm rather than the Freundlich equation,indicating the monolayer adsorption of MB.(4)We prepared the porous rice husk/MnFe2O4(RMN)and rice husk/CoFe2O4 nanocomposite(RCN)with high BET surface area and pore volume,and revealed their catalytic degradation capacity for MB assisted by microwave(Chapter V).The MB removal fits pseudo-second-order model.The removal rate increases with sample dosage,microwave output power,and initial pH value.The resulting pH value was inclined to neutral after microwave treatment.The dimethylamino including methyl groups in MB molecule are easier and prior to be degraded by RMN and RCN during either adsorption or microwave treatments.According to the resulting concentrations of MB,NO3-and SO42-,the maximum MB removal achieved 55.0%and 99.7%by RMN and RCN,respectively,among which more than 22.1%and 46.8%were completely degraded.(5)We introduced a microwave enhanced Fenton process to remove MB from aqueous solution(Chapter VI).The conversion rate of methylene blue(MB)was increased and accelerated due to the assistance of microwave irradiation,with value of 93.0%after heated for only 1 min,even higher than that of treated by traditional Fenton process for 65 min.The MB conversion increases with initial conversations of H2O2 and Fe2+ because of the increased generation of hydroxyl radicals.The MB conversion changes slightly with pH at values of below 7 and declines dramatically when the pH is higher than 8,with optimum pH value of about 3.During the microwave treatment,the maximum UV-vis absorption peak decreased much quicker than that of other two peaks,and blue shifted form wavelength of 664-629 nm,indicating the decomposition of dimethylamino and methyl groups in MB molecules.