The work aims to study the removal of crystal violet (CV) using laterite soil with surface modification by surfactant (SML). Surface modification of laterite soil was conducted by pre-adsorption of sodium dodecyl sulfate (SDS) at pH 4 and low ionic strength to enhance removal of CV. The effective conditions for CV removal through adsorption technique using SML were optimized and found to be contact time 60 min, pH 6, adsorbent dosage 5 mg/mL, and 5 mM NaCl as background electrolyte. The highest removal of CV using SML reached to 86.5% under optimum conditions. We used Fourier transform infrared spectroscopy (FT-IR) to evaluate the change of surface vibrational groups of laterite after SDS pre-adsorption and after CV adsorption while the different charged surface was determined by ζ potential measurements. The CV adsorption onto SML increased when increasing ionic strength from 1 to 10 mM. Nevertheless, at high ionic strength, this trend is reversal due to desorption of SDS from laterite surfaces. Adsorption isotherms of CV onto SML at different NaCl concentrations were tried to fit by Langmuir, Freundlich, and a two-step adsorption models. The adsorption kinetics were in good agreement with pseudo-second-order model. The removal efficiency of CV after four regenerations still reached higher than 85%. On the basis of adsorption isotherms, charged surface change by ζ potential and surface modification by FT-IR, we suggest that CV adsorption onto SML was induced by both non-electrostatic and electrostatic interactions. We also demonstrate that SML is a novel, reusable, and low-cost adsorbent for cationic dye removal from aqueous solution.

中文翻译：

---

表面修饰的红土土壤，用阴离子表面活性剂从水溶液中去除阳离子染料（结晶紫）

这项工作旨在研究使用表面活性剂（SML）进行表面改性的红土土壤去除结晶紫（CV）的方法。通过在pH 4和低离子强度下预吸附十二烷基硫酸钠（SDS）进行红土土壤的表面改性，以提高CV的去除率。优化了使用SML通过吸附技术去除CV的有效条件，发现其接触时间为60分钟，pH为6，吸附剂剂量为5 mg / mL和5 mM NaCl作为背景电解质。在最佳条件下，使用SML去除CV的最高值达到86.5％。我们使用傅里叶变换红外光谱（FT-IR）评估了SDS预吸附后和CV吸附后红土的表面振动基团的变化，而不同的带电表面是通过ζ电位测量确定的。当离子强度从1 mM增加到10 mM时，SV上的CV吸附增加。然而，在高离子强度下，由于SDS从红土表面解吸，这种趋势得以逆转。Langmuir，Freundlich和两步吸附模型试图拟合CV在不同NaCl浓度下对SML的吸附等温线。吸附动力学与拟二级模型吻合良好。四次再生后CV的去除率仍达到85％以上。根据吸附等温线，ζ电位的带电表面变化和FT-IR的表面改性，我们认为CV吸附到SML上是由非静电和静电相互作用引起的。我们还证明SML是一种新颖，可重复使用且低成本的吸附剂，用于从水溶液中去除阳离子染料。