BACKGROUND Organic dye pollution in water has become a major source of environmental pollution. Mn(III/IV) oxides have attracted a great deal of attention to remove organic dye pollutants due to their unique structures and physicochemical properties. Numerous studies have reported the removal of dye by various Mn(III/IV) oxides through catalytic degradation and adsorption. The crystalline structures of manganese oxides and solution pH may exert substantial impact on the removal of dyes. However, few studies have focused on the oxidative degradation of RhB dye using Mn(III/IV) oxides with different crystal structures during a spontaneous reaction. In the present study, three manganese oxides with different crystal type (α-MnO2, β-MnO2, and δ-MnO2) were prepared by refluxing process to decolorize RhB dye in various pH solutions. RESULTS The results showed that the decolorization efficiencies of RhB for the three manganese oxides all increase with decrease solution pH. α-MnO2 exhibited highest activity and could efficiently degrade RhB at pH 2-6. The degradation of RhB by β-MnO2 and δ-MnO2 could be observed at pH 2-3, and only little adsorption RhB on manganese oxides could be found at pH 4-6. The UPLC/MS analysis suggests that the decolorization of RhB by manganese oxides consists of three main stages: (1) cleavage of the ethyl groups from RhB molecular to form Rh; (2) further destruction of -COOH and -CNH2 from Rh to form the small molecular substances; (3) mineralization of the small molecular substances into CO2, H2O, NO3 (-) and NH4 (+). CONCLUSIONS Overall, these results indicate that α-MnO2 may be envisaged as efficient oxidants for the treatment of organic dye-containing wastewater under acid conditions.

中文翻译：

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锰氧化物对RhB染料的脱色：晶体类型和溶液pH的影响。

背景技术水中的有机染料污染已经成为环境污染的主要来源。Mn（III / IV）氧化物因其独特的结构和理化性质而吸引了广泛的关注，以去除有机染料污染物。大量研究报道了通过催化降解和吸附作用，各种Mn（III / IV）氧化物去除了染料。锰氧化物的晶体结构和溶液的pH值可能会对染料的去除产生重大影响。然而，很少有研究集中在自发反应过程中使用具有不同晶体结构的Mn（III / IV）氧化物对RhB染料的氧化降解。在本研究中，通过回流工艺制备了三种不同晶体类型的锰氧化物（α-MnO2，β-MnO2和δ-MnO2），以在各种pH溶液中使RhB染料脱色。结果结果表明，RhB对三种锰氧化物的脱色效率均随溶液pH值的降低而增加。α-MnO2表现出最高的活性，并可以在pH 2-6下有效降解RhB。在pH 2-3时，可以观察到β-MnO2和δ-MnO2对RhB的降解，在pH 4-6时，仅发现很少的RhB在锰氧化物上的吸附。UPLC / MS分析表明，锰氧化物对RhB的脱色包括三个主要阶段：（1）将乙基从RhB分子上裂解形成Rh。（2）进一步从Rh破坏-COOH和-CNH2，形成小分子物质；（3）将小分子物质矿化为CO2，H2O，NO3（-）和NH4（+）。结论总体而言，