Deka Bharati, Bhattacharyya K G
Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India.
Department of Chemistry, Gauhati University, Guwahati 781014, Assam, India.
J Environ Manage. 2015 Mar 1;150:479-488. doi: 10.1016/j.jenvman.2014.12.037. Epub 2015 Jan 3.
In this work, Mn(II), Co(II) and Ni(II) were incorporated into waste coal fly ash used as a catalyst support by refluxing with the appropriate aqueous salt solution. The materials were calcined at 773-873 K for 5 h and the amount of divalent cations entering into the fly ash was determined by AAS measurements. Further characterization included estimation of oxides by XRF, structural properties by XRD, topographical features by SEM, surface functional groups by FT-IR, surface area and pore dimensions by BET N2-adsorption isotherms. The efficiency of the materials as environmental oxidation catalysts were tested with respect to destruction of 4-chlorophenol (4-CP) in water in the presence of hydrogen peroxide. Considered as one of the most persistent, toxic and largely applied organic compound, 4-CP enters water from the effluents of petrochemical, plastic, pesticide, kraft mill and other organochemical industries and research centers. Wet oxidation of 4-CP was tested by varying the mole ratio of 4-CP and H2O2, catalyst load, temperature, reaction time, 4-CP concentration and pH. Oxidation of 4-CP (5 × 10(-3) M or 643 mg L(-1)) was 51.1% for Mn(II)-fly ash, 58.3% for Co(II)-fly ash and 61.0% for Ni(II)-fly ash after 180 min at 323 K with 4-CP: H2O2 mole ratio of 1:1. COD load of the reaction mixture (4-CP: 5 × 10(-3) M, H2O2: 5 × 10(-3) M, catalyst load: 1.0 g L(-1), temperature 323 K, reaction time 0-240 min) decreased from 1480 to 620, 380, and 140 mg L(-1) respectively after oxidation with Mn(II)-fly ash, Co(II)-fly ash and Ni(II)-fly ash (overall COD reduction was 58.0, 74.3 and 90.5% respectively). The oxidation followed second order kinetics with the average rate coefficient of 7.9, 1.3 and 1.2 L mol(-1) min(-1) for Mn(II)-, Co(II)- and Ni(II)-fly ash. Increase in H2O2: 4-CP mole ratio from 1:1 to 20:1 (reaction time 300 min, catalyst load 1.0 g L(-1)) enhanced destruction from 52.1 to 95.6% for Mn(II)-fly ash, 58.3-95.6% for Co(II)-fly ash and from 60.4 to 94.8% for Ni(II)-fly ash. The oxidation increased with catalyst load but very high loads were not effective. Low pH favored the oxidation, but the catalysts performed well at the pH of aqueous 4-CP solution. A mechanism for the reactions is suggested based on the analysis of the products of oxidation.
在本研究中，通过与适当的盐水溶液回流，将锰（II）、钴（II）和镍（II）掺入用作催化剂载体的废弃煤飞灰中。材料在773 - 873 K下煅烧5小时，并通过原子吸收光谱（AAS）测量确定进入飞灰的二价阳离子量。进一步的表征包括通过X射线荧光光谱（XRF）估算氧化物、通过X射线衍射（XRD）分析结构性质、通过扫描电子显微镜（SEM）观察形貌特征、通过傅里叶变换红外光谱（FT - IR）分析表面官能团、通过BET N₂吸附等温线测定表面积和孔径。在过氧化氢存在下，测试了这些材料作为环境氧化催化剂对水中4 - 氯苯酚（4 - CP）的降解效率。4 - CP被认为是最持久、有毒且广泛应用的有机化合物之一，它从石化、塑料、农药、牛皮纸造纸厂以及其他有机化学工业和研究中心的废水中进入水体。通过改变4 - CP与H₂O₂的摩尔比、催化剂负载量、温度、反应时间、4 - CP浓度和pH值，测试了4 - CP的湿式氧化。在323 K下，4 - CP（5×10⁻³ M或643 mg L⁻¹）与H₂O₂摩尔比为1:1，反应180分钟后，锰（II） - 飞灰对4 - CP的氧化率为51.1%，钴（II） - 飞灰为58.3%，镍（II） - 飞灰为61.0%。反应混合物（4 - CP：5×10⁻³ M；H₂O₂：5×10⁻³ M；催化剂负载量：1.0 g L⁻¹；温度323 K；反应时间0 - 240分钟）经锰（II） - 飞灰、钴（II） - 飞灰和镍（II） - 飞灰氧化后，化学需氧量（COD）负载分别从1480降至620、380和140 mg L⁻¹（总体COD降低分别为58.0%、74.3%和90.5%）。氧化反应遵循二级动力学，锰（II） - 飞灰、钴（II） - 飞灰和镍（II） - 飞灰的平均速率系数分别为7.9、1.3和1.2 L mol⁻¹ min⁻¹。将H₂O₂与4 - CP的摩尔比从1:1增加到20:1（反应时间300分钟，催化剂负载量1.0 g L⁻¹），锰（II） - 飞灰对4 - CP的降解率从52.1%提高到95.6%，钴（II） - 飞灰从58.3%提高到95.6%，镍（II） - 飞灰从60.4%提高到94.8%。氧化率随催化剂负载量增加而提高，但过高负载无效。低pH值有利于氧化反应，但催化剂在4 - CP水溶液的pH值下表现良好。基于氧化产物的分析，提出了反应机理。
