The Synthesis of Catalysts for the Degradation of Organic Wastewater and Study on the Catalytic Reaction Mechanisms

Author:He Shuai Ming

Supervisor:li jun


Degree Year:2019





Water pollution is one of the most serious challenges facing human society.Among the various pollutants present in water,refractory organic pollutants have attracted more attention due to their high toxicity,and generally simple biological treatment cannot meet the national emission standards.In this paper,the refractory industrial organic wastewater(recalcitrant paper-making wastewater)and the model organic pollutant methylene blue solution were chosen as research subject.The effects of catalytic ozone oxidation and Pd@wood catalysts on the degradation efficiency of paper-making wastewater and the methylene blue solution were discussed,respectively.In this study,Fe supported on activated carbon(Fe@AC)was prepared and used as a catalyst in the catalytic ozonation of pulp and paper mill effluent.The activity of this catalyst was studied in terms of color and chemical oxygen demand(COD)removal efficiency.Results showed that the COD removal rate was increased by 21%in the presence of the Fe@AC catalyst.After 60 min of ozonation of the pulp and paper mill effluent,COD removal rates reached 56%in the presence of Fe@AC,43%using AC as catalyst,and only 35%with ozonation alone.Ozone alone can achieve satisfactory color removal results.Owing to the scavenging effect of carbonate and bicarbonate ions towards hydroxyl radicals,the COD removal rate in Fe/AC catalytic ozonation of the effluent was strongly inhibited in the presence of these two ions.The present work utilized a Fe/γ-Al2O3 catalytic ozonation process for tertiary treatment of actual paper-making wastewater.Results indicated that in comparison to ozone alone,the addition of a Fe/γ-Al2O3 catalyst enhanced the removal efficiency of TOC during ozonation after 60 min of treatment,which initiated a 25%enhancement for TOC removal.After 60 min of treatment,TOC removal rates reached 51%using Fe/γ-Al2O3 as a catalyst,37%in the presence ofγ-Al2O3 and only 26%with ozonation alone,which already showed excellent color removal results.The presence of tert-butanol(a well-known hydroxyl radical scavenger)had a negative effect on the TOC removal rate of the Fe/γ-Al2O3/O3 process,indicating that the Fe/γ-Al2O3/O3 process follows a hydroxyl radical(·OH)reaction mechanism.Finally,the prepared Fe/γ-Al2O3 catalyst exhibited good stability and recyclability.These results illustrate that there are potential applications of ozonation catalyzed by Fe/Al2O3 for the tertiary treatment of biologically recalcitrant wastewater.This study developed a novel copper-cerium oxide supported alumina(Cu-Ce/Al2O3)catalyst for the catalytic ozonation of pulp and paper mill wastewater.The evenly distributed composite metal oxides on the surface of catalysts evidently improved the catalytic degradation efficiency.The Cu-Ce/Al2O3/O3 process increased the total organic carbon(TOC)removal by 6.5%,9.5%,24.5%and 35.5%,compared with Ce/Al2O3/O3,Cu/Al2O3/O3,Al2O3/O3,and ozone alone processes,respectively.The enhanced catalytic ozonation efficiency was mainly ascribed to an increased hydroxyl radical(·OH)-mediated ozonation,both in the bulk solution and on the surface of catalysts.The surface hydroxyl groups(-OHs)of Al2O3 along with the deposited Cu-Ce oxides greatly enhanced the catalytic performance.This work illustrated potential applications of Cu-Ce/Al2O3 catalyzed ozonation for the advanced treatment of biologically recalcitrant wastewaters.Wood,a natural material,possesses a unique hierarchal 3D interconnected microstructure featuring vertically aligned microchannels(vessels and lumina)along the tree growth direction that are lined with micropores(pits,nanopores,and ray cells).This structure renders wood highly desirable for a wide range of emerging applications and particularly as a cost-effective separation membrane material.Herein,we demonstrate a novel cross-flow filtration device based on a wood membrane decorated with Pd nanoparticles,in which the wastewater moves perpendicular to the tree-growth direction through ray cells,pits and nanopores,as well as along the tree-growth direction through the vessel channels and tracheids.In this manner we achieve strong organic contaminant-catalyst interactions by the turbulence that is generated as the wastewater flows through the small diameter micropores and along the microchannel structure.Consequently,the membrane exhibits excellent wastewater treatment performance with a high flow rate of up to 1.1×105 L·m-2·h-1,a high degradation efficiency of99.8%,and a high turnover frequency of 2.2 mol MB·molPd-1·min-1,representing the highest value among various reported Pd-based catalyst devices.This high-performance wood-based cross-flow filtration device provides a new material platform for rapid high concentration wastewater treatment and can be extended to other potential separation applications,such as heavy metal removal,water disinfection,and desalination.