响应曲面法优化油茶饼对活性红15的生物吸附特征及机理

基于“以废治废”的理念,以农林业废弃物——油茶饼为原料制备生物吸附剂,吸附去除废水中的RR15(C.I. Reactive Red 15,活性红15)染料,并采用响应曲面法中的Box-Behnken设计对油茶饼生物吸附剂吸附RR15的条件进行优化. 结果表明:pH对油茶饼生物吸附剂吸附RR15的吸附容量和去除率均有显著影响(P<0.000 1)；当pH为1.0、初始ρ(RR15)为300 mg/L、吸附温度为20 ℃时,油茶饼生物吸附剂对RR15的吸附效果最佳. 相比于Langmuir和Freundlich吸附等温线模型,Temkin吸附等温线模型可以更好地描述油茶饼生物吸附剂对RR15的吸附平衡数据. 吸附温度为20 ℃时,由Langmuir吸附等温线模型计算得到的Q0(吸附剂的单层饱和吸附量)为74.63 mg/g. 动力学分析显示,油茶饼生物吸附剂对RR15的吸附过程符合准二级动力学模型(R2>0.999 7),支持了限速步骤是化学吸附的理论；内部扩散和边界层扩散都可能影响吸附速率. 热力学分析表明,该吸附过程是一个自发的放热过程. FTIR(fourier transform infrared spectroscopy,傅里叶变换红外光谱)分析发现,油茶饼生物吸附剂上羟基、胺基等官能团可能是RR15染料的主要结合位点. 研究显示,油茶饼生物吸附剂是一种具有潜力的绿色吸附剂,可以有效去除废水中的RR15染料. 

Reactive Red 15 Biosorption on Oil-Tea Cake:Optimization Using Response Surface Methodology and Mechanism

Based on the concept of waste control by waste, agroforestry waste oil-tea cake was used to remove azo dye Reactive Red 15 (RR15) via biosorption from aqueous solution. To optimize the biosorption condition, a Box-Behnken Design with a response surface methodology was carried out. Three independent variables-pH, initial RR15 concentration and biosorption temperature-were studied, and biosorption capacity and removal efficiency were set as the response values. Statistical analysis showed that pH was highly significant for both biosorption capacity and removal efficiency (P<0.0001); the optimal biosorption condition was pH 1.0, initial RR15 concentration 300 mg/L and biosorption temperature 20 ℃. The Temkin isotherm model was more applicable for describing the biosorption equilibrium data in the whole initial RR15 concentration range than the Freundlich or Langmuir isotherm model. Q0 gained from Langmuir isotherm model at 20 ℃ was 74.63 mg/g. The kinetic study showed that the experimental data were well fitted by the pseudo-second-order model (R2>0.9997), which indicated that the dominant biosorption belonged to the chemisorptive nature. Both intra-particle diffusion and boundary layer diffusion might affect the biosorption rate. Thermodynamic study demonstrated that the biosorption was a spontaneous and exothermic process. To understand the mechanical behavior of RR15 biosorption process, SEM, EDS and FTIR were employed to characterize the oil-tea cake pre- and post-biosorption. The FTIR analysis indicated that functional groups (e.g., amine, hydroxyl) on the oil-tea cake biosorbent were the active binding sites for the RR15 biosorption. These results showed that oil-tea cake is a promising biosorbent, which could effectively remove RR15 from dye wastewater.