ABSTRACT

Transition metal oxides have been applied to degrade organic dyes found in water bodies via photocatalysis. To do it, however, is essential that the dye molecules adsorb onto the metal oxide surface. Thus, optimizing the adsorption capacity of the adsorbent increases the probability of reaction between oxidation radicals and organic dye molecules and maximizes the effectiveness per gram of photocatalyst. With this in mind, we studied the adsorption behavior of Methylene Blue (MB) and Acid Orange 7 (AO7), two commonly found pollutants, as a function of dilution’s pH, WO₃ load, and initial dye concentration. We found out that WO₃ adsorbs up to 80% of MB at pH = 6, and 13% of AO7 at pH = 2, although it is unable to adsorb AO7 at the natural pH of the dye dilution. Assuming a pseudo-second order kinetics model for the analysis of the MB adsorption amount, we determined a rate constant k₂ = 6 × 10⁻²(g · mg⁻¹)/min for the adsorption process. We put forward a molecular model for adsorption, driven by concentration gradients and electrostatic interactions. Finally, from a statistical analysis, we determined that pH is the most significant factor for the adsorption of MB and AO7 on WO₃, reinforcing the notion that electrostatic interactions are the main mechanism driving the adsorption process. The Box–Behnken design optimization also evinces the key playing role of WO₃ load in the adsorption percentage of AO7 and let us establish the optimal load required to maximize adsorption.

摘要

过渡金属氧化物已被用于通过光催化降解水体中的有机染料。然而，要做到这一点，染料分子必须吸附在金属氧化物表面上。因此，优化吸附剂的吸附容量会增加氧化自由基和有机染料分子之间的反应概率，并使每克光催化剂的效率最大化。考虑到这一点，我们研究了亚甲基蓝 (MB) 和酸性橙 7 (AO7) 这两种常见污染物的吸附行为，作为稀释液的 pH 值、WO ₃负载和初始染料浓度的函数。我们发现WO ₃在 pH = 6 时吸附高达 80% 的 MB，在 pH = 2 时吸附高达 13% 的 AO7，尽管它无法在染料稀释液的自然 pH 值下吸附 AO7。假设用于分析MB吸附量的准二级动力学模型，我们确定吸附过程的速率常数k ₂  = 6 × 10 ^-2 (g·mg ^-1 )/min。我们提出了由浓度梯度和静电相互作用驱动的吸附分子模型。最后，通过统计分析，我们确定 pH 是 MB 和 AO7 在 WO _{3上吸附的最重要因素}，强化了静电相互作用是驱动吸附过程的主要机制的观点。_{Box-Behnken 设计优化也证明了 WO 3}负载在 AO7 吸附百分比中的关键作用，让我们确定最大化吸附所需的最佳负载。