废报纸生物质炭的制备及对铜离子的吸附性能

Biochar derived from waste newspapers for removing copper ions from aqueous solution

【目的】以废报纸为原料,通过氮气(N2)保护在不同热解温度下制备生物质炭,并探讨废报纸基生物质炭对铜离子(Cu^2+)的吸附性能和吸附机制。【方法】采用元素分析、比表面积分析仪(BET)、傅里叶红外光谱(FTIR)、X射线光电子能谱(XPS)、扫描电镜(SEM)、X射线衍射仪(XRD)和原子吸收光谱仪(AAS)等对生物质炭进行表征。【结果】所制备的生物质炭具有多孔结构,比表面积高(211 m^2·g^-1),有利于从水中去除Cu^2+。生物质炭的物理和化学性质随着热解温度的变化而变化。随着热解温度的升高,生物质炭的芳香性、比表面积、pH和灰分含量逐渐增加,而氢、氮和氧含量下降。同时进行批量吸附试验,分析溶液初始pH、吸附时间、初始浓度、不同吸附温度对生物质炭吸附容量的影响。热解温度为400、500、600℃的生物质炭在30℃、pH为5.0的条件下最大吸附容量分别为107、115和138 mg·g^-1。伪二级动力学模型和Langmuir等温吸附模型能很好地模拟吸附过程,表明在此吸附过程中,化学吸附是限速步骤,吸附发生在吸附剂内特定的均相位点(单层吸附)。通过热力学模型计算所得ΔHo为正值,表明吸附过程是吸热反应。此外,生物质炭的吸附机制包括沉淀作用、离子交换、π-π作用和络合反应。【结论】本研究以废报纸为原料,所制备的生物质炭是具有一定应用前景的、环境友好的、高效的Cu^2+吸附材料。

[Objective]A series kinds of biochar were produced from waste newspapers by pyrolysis at different temperatures(400,500 and 600℃).The ability of removing copper ions from an aqueous solution of these biochar will be testified and the corresponding adsorbing mechanism also will be discussed.[Method]The following techniques have been utilized to characterize the structure and properties of biochar,which are elemental analysis,Brunauer-Emmett-Teller method(BET),Fourier transform-infrared spectroscopy(FTIR),X-ray photoelectron spectrometry(XPS),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),and atomic absorption spectroscopy(AAS).[Result]The fabricated biochar(WBC-600)exhibits a typical porous structure and its specific surface area is high as 211 m^2·g^-1.This structure will be beneficial for removing Cu^2+from aqueous solution.Furthermore,physical and chemical properties of biochar varied significantly based on the pyrolysis temperatures.It is revealed that the aromaticity,specific surface area,pH,and ash content of the biochar increased gradually with the increasing pyrolysis temperature,while the hydrogen,nitrogen and oxygen contents decreased.Batch adsorption experiments were performed to examine the effects of initial pH,contact time,Cu^2+concentration,and temperature on the adsorption capacity of Cu^2+.The maximum adsorption capacities of waste newspapers biochar,WBC-400,WBC-500,and WBC-600 were 107,115 and 138 mg·g^-1 at 30℃(pH 5.0),respectively.The pseudo-second-order kinetics model and Langmuir adsorption isotherm model were suitable for describing the adsorption process,indicating that chemical sorption was a rate-limiting step and adsorption took place at specific homogeneous sites within the adsorbent(monolayer adsorption).The calculatedΔHo values indicated that the adsorption process was endothermic.Furthermore,the adsorption mechanism for WBC was attributed to precipitation,ion exchange,π—πinteractions,and complexation.[Conclusion]The biochar fabricated from waste newspapers by the process suggested in our study meets the criterion of being an effective adsorbent for removing Cu^2+from an aqueous solution.Moreover,since the original material,waste newspaper,is a typical solid waste disposal,the manufacturing of the biochar will have benefits both to reduce cost and protect environment.