Heterogeneous catalytic wet peroxide oxidation of phenol over delaminated Fe–Ti-PILC employing microwave irradiation

Catalytic wet peroxide oxidation of phenol through mesoporous silica-pillared clays supported iron and/or titanium incorporated catalysts

Catalytic performances of Silica Pillared Clay (SPC) supports synthesized in different silica amounts both from standard SWy-2 clay mineral and Hançılı region bentonite rock (HWB), and iron (Fe) and/or titanium (Ti) incorporated SPCs in different combinations were evaluated in various advanced Catalytic Wet Peroxide Oxidation (CWPO) of phenol. Host clay mineral type led to different oxidation performances and metal loading created significant increases in the catalytic performance. CWPO performance of Fe-loaded SPCs was better than Ti-loaded ones, so oxidation parameters for Fe-SPCs were studied in detail. Catalyst amount and rise in temperature increased phenol conversion values significantly, and catalysts were more effective in lower pH reaction medium. Aromatic intermediates such as catechol, hydroquinone and benzoquinone formed at the beginning of oxidation were oxidized to carboxylic acids with an advancing oxidation time. The presence of carboxylic acids such as oxalic and formic acid resulted in relatively low total organic carbon (TOC) conversion values. The highest catalytic activity was obtained with high silica content Fe-SPCs synthesized with both host clays. Complete conversion was nearly achieved within 60 min with an experimental condition of T = 30 °C, pH = 3.7 and catalyst/solution ratio = 2 g/L for SWy-2 based catalyst by applying either CWPO or PCWPO (Photo Catalytic Wet Peroxide Oxidation) techniques. SCWPO (Sono Catalytic Wet Peroxide Oxidation) technique also yielded this value at the same oxidation conditions for HWB based catalyst. TOC conversion values at 240 min oxidation time were determined as 33% and 48% for SWy-2 based catalyst with CWPO and PCWPO techniques, respectively, and 37% for HWB based catalyst with SCWPO technique. SWy-2 based catalyst still retained its performance after 3 cycles.

The advantages of clay mineral modification methods for enhancing adsorption efficiency in wastewater treatment: a review

This review discusses the recent trends in the research over the last 30 years to use clay minerals in natural and modified forms for removing different toxic organic/inorganic pollutants. The natural and modified forms of clay minerals have an exceptional ability to remove different contaminants. However, the modification methods can improve the clay mineral adsorption properties that consequently increase more adsorption sites and functional groups to adsorb different environmental pollutants. This review shows the importance of modification methods and more extension of novel clay preparation based on nanotechnology which could raise the control of pollution. The syntheses of functionalized clays such as pillared clays and porous clay heterostructures introduce the new class of heterostructure materials with high adsorption capacity, capability, and selectivity. Due to the acceptable properties of heterostructure materials including high specific surface area, thermal and mechanical stability, and the existence of multifunctional groups to selective adsorption, this review collects more literature of research related to environmental protection issues. However, it is expected much attention to get a better understanding of the adsorption mechanism, regeneration, and recovery process of these materials.

Current status of applying microwave-associated catalysis for the degradation of organics in aqueous phase - A review

Interactions between microwaves and certain catalysts can lead to efficient, energy-directed convergence of a relatively dispersed microwave field onto the reactive sites of the catalyst, which produces thermal or discharge effects around the catalyst. These interactions form "high-energy sites" (HeS) that promote energy efficient utilization and enhanced in situ degradation of organic pollutants. This article focuses on the processes occurring between microwaves and absorbing catalysts, and presents a critical review of microwave-absorbing mechanisms. This article also discusses aqueous phase applications of relevant catalysts (iron-based, carbon-based, soft magnetic, rare earth, and other types) and microwaves, special effects caused by the dimensions and structures of catalytic materials, and the optimization and design of relevant reactors for microwave-assisted catalysis of wastewater. The results of this study demonstrate that microwave-assisted catalysis can effectively enhance the degradation rate of organic compounds in an aqueous phase and has potential applications to a variety of engineering fields such as microwave-assisted pyrolysis, pollutant removal, material synthesis, and water treatment.

Layer like porous materials with hierarchical structure

Many chemical compositions produce layered solids consisting of extended sheets with thickness not greater than a few nanometers. The layers are weakly bonded together in a crystal and can be modified into various nanoarchitectures including porous hierarchical structures. Several classes of 2-dimensional (2D) materials have been extensively studied and developed because of their potential usefulness as catalysts and sorbents. They are discussed in this review with focus on clays, layered transition metal oxides, silicates, layered double hydroxides, metal(iv) phosphates and phosphonates, especially zirconium, and zeolites. Pillaring and delamination are the primary methods for structural modification and pore tailoring. The reported approaches are described and compared for the different classes of materials. The methods of characterization include identification by X-ray diffraction and microscopy, pore size analysis and activity assessment by IR spectroscopy and catalytic testing. The discovery of layered zeolites was a fundamental breakthrough that created unprecedented opportunities because of (i) inherent strong acid sites that make them very active catalytically, (ii) porosity through the layers and (iii) bridging of 2D and 3D structures. Approximately 16 different types of layered zeolite structures and modifications have been identified as distinct forms. It is also expected that many among the over 200 recognized zeolite frameworks can produce layered precursors. Additional advances enabled by 2D zeolites include synthesis of layered materials by design, hierarchical structures obtained by direct synthesis and top-down preparation of layered materials from 3D frameworks.

Application of Response Surface Methodology to Enhance Phenol Removal from Refinery Wastewater by Microwave Process

Phenol contaminated petroleum refinery wastewater presents a great threat on water resources safety. This study investigates the effect of microwave irradiation on removal of different concentrations of phenol in an attempt for petroleum refinery wastewater treatment. The obtained results show that the MW output power and irradiation time have a significant positive effect on the removal efficiency of phenol. The kinetic reaction is significantly affected by initial MW output power and initial phenol concentrations. Response surface methodology (RSM) was employed to optimize and study the interaction effects of process parameters: MW output power, irradiation time, salinity, pH, and H2O2 concentration using central composite design (CCD). From the CCD design matrix, a quadratic model was considered as an ultimate model (R2 = 0.75) and its adequacy was justified through analysis of variance (ANOVA). The overall reaction rates were significantly enhanced in the combined MW/H2O2 system as proved by RSM. The optimum values for the design parameters of the MW/H2O2 process were evaluated giving predicted phenol removal percentage of 72.90% through RSM by differential approximation and were confirmed by experimental phenol removal of 75.70% in a batch experiment at optimum conditions of 439 W MW power, irradiation time of 24.22 min, salinity of 574 mg/L, pH 5.10, and initial H2O2 concentration of 10% (v/v).

High efficiency degradation of 4-nitrophenol by microwave-enhanced catalytic method

Application of the microwave-enhanced catalytic degradation (MECD) method on the abatement of 4-nitrophenol (4-NP) using nickel oxide was studied. A mix-valenced nickel oxide was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite with/without microwave-assisted heating. They were characterized by X-ray (XRD), infrared spectroscopy (IR), temperature programmed reduction (TPR), and transmission electron micrographs (TEM). Their catalytic activities towards the degradation of 4-NP were investigated through continuous bubbling of air during the liquid phase and evaluated quantitatively with high pressure liquid chromatography (HPLC). Also, the effect of the kinds of catalyst, temperature, pH, initial concentration, and dosage of catalyst on the efficiency of 4-NP degradation was investigated. The results showed that the 4-NP was completely degraded using the high efficiency MECD method within 15 min under [H(+)] = 1.0M, T = 40 °C, and C = 200 ppm over nickel oxide.

Preparation of Fe-Cu catalysts and treatment of a wastewater mixture by microwave-assisted UV catalytic oxidation processes

Microwave-assisted UV catalytic oxidation (MW/UV) is a potential method to treat organic pollutants that have non-biological degradability and high toxicity. To achieve high treatment efficiency, it is crucial to prepare heterogeneous photocatalysts with a high activity. Iron-copper catalysts were prepared by four different methods. Synthetic wastewater containing aniline and nitrophenol (TOC = 1000 mg/L) was treated. The key parameters including the proportion of Fe2O3 and CuO and the total content of the active components are discussed. The optimum catalyst dosage and the whole catalytic oxidation process were investigated, and different catalytic oxidation systems were also compared. The catalyst prepared by impregnation was best: the highest TOC removal efficiency reached 78%. The optimum proportion of Fe2O3 and CuO and the content of the total active composition were 4:1 and 30%, respectively. The catalyst preparation method had a greater influence on the MW/UV system than on the microwave (MW) system, and the synergistic effect between MW and UV was verified. The MW/UV system was more susceptible to catalyst dosage than was the MW system, and the optimum catalyst dosage was 5 g/L. The catalyst and H2O2 had a synergistic effect. The presence of a possible non-thermal microwave effect could be expected.

P-chlorophenol wastewater treatment by microwave-enhanced catalytic wet peroxide oxidation

A microwave-enhanced catalytic wet peroxide oxidation (MW-CWPO) technology was investigated to treat a high concentration of p-chlorophenol wastewater under a mild condition. The MW-CWPO experiments were carried out in a microwave autoclave using copper(II) oxide (CuO)-loaded active carbon as a catalyst. The p-chlorophenol was directly ring-opened within 5 minutes at 343 K and 0.3 MPa and then mineralized to carbon dioxide and water. More than 90% of the total organic carbon was removed within 15 minutes. The reaction activation energy (Ea) of hydrogen peroxide (H2O2) decomposition was decreased from 47.7 to 43.1 kJ/mol under microwave irradiation. The H2O2 catalytic decomposition was fitted to a second-order reaction under microwave irradiation, while it followed a first-order reaction without microwave irradiation. The experimental results indicate that the MW-CWPO method has significant potential applications for a high concentration of p-chlorophenol wastewater.

Microwave-enhanced catalytic degradation of 4-chlorophenol over nickel oxides under low temperature

Microwave-enhance catalytic degradation (MECD) of 4-chlorophenol (4-CP) using nickel oxide was studied. A mix-valenced nickel oxide was obtained from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite (assigned as PO). Then, the as-prepared PO was irradiated under microwave irradiation to fabricate a high active mix-valenced nickel oxide (assigned as POM). Further, pure nanosized nickel oxide was obtained from the POM by calcination at 300, 400 and 500 degrees C (labeled as C300, C400 and C500, respectively). They were characterized by X-ray (XRD), infrared spectroscopy (IR) and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of 4-CP on the efficiency of the degradation were further investigated under continuous bubbling of air through the liquid-phase and quantitative evaluation by high pressure liquid chromatography (HPLC). Also, the effects of temperature, pH and kinds of catalysts on the efficiency of the degradation have been investigated. The results showed that the 4-CP was degraded completely by MECD method within 20 min under pH 7, T=40 degrees C and C=200 g dm(-3) over POM catalyst. The relative activity was affected significantly with the oxidation state of nickel.

Catalytic activity of CuOn-La2O3/gamma-Al2O3 for microwave assisted ClO2 catalytic oxidation of phenol wastewater

In order to develop a catalyst with high activity and stability for microwave assisted ClO2 catalytic oxidation, we prepared CuOn-La2O3/gamma-Al2O3 by impregnation-deposition method, and determined its properties using BET, XRF, XPS and chemical analysis techniques. The test results show that, better thermal ability of gamma-Al2O3 and high loading of Cu in the catalyst can be achieved by adding La2O3. The microwave assisted ClO2 catalytic oxidation process with CuOn-La2O3/gamma-Al2O3 used as catalyst was also investigated, and the results show that the catalyst has an excellent catalytic activity in treating synthetic wastewater containing 100 mg/L phenol, and 91.66% of phenol and 50.35% of total organic carbon (TOC) can be removed under the optimum process conditions. Compared with no catalyst process, CuOn-La2O3/gamma-Al2O3 can effectively degrade contaminants in short reaction time and with low oxidant dosage, extensive pH range. The comparison of phenol removal efficiency in the different process indicates that microwave irradiation and catalyst work together to oxidize phenol effectively. It can therefore be concluded from results and discussion that CuOn-La2O3/gamma-Al2O3 is a suitable catalyst in microwave assisted ClO2 catalytic oxidation process.

Wet peroxide oxidation of chlorophenols

This study evaluates the application of Wet Peroxide Oxidation (WPO) for the treatment of solutions containing 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP). These compounds are of special interest due to their high toxicity and low biodegradability. WPO is included in the Advanced Oxidation Processes, which are technologies based on an initial formation of hydroxyl radicals that further oxidize the organic matter. The influence of some operating conditions such as temperature, dosage of hydrogen peroxide and initial concentration of the chlorophenols was studied in absence of a catalyst. The results of this study prove that 4-CP and 2,4-DCP can be completely removed from wastewaters by means of WPO. Total Organic Carbon (TOC) and 4-CP removals of 72.3% and 100%, respectively, were achieved working at 100 degrees C with 2.5 mL of H(2)O(2) and an initial concentration of 500 ppm of 4-CP after 90 min of reaction. Under the same conditions but with an initial concentration of 500 ppm of 2,4-DCP a TOC removal of 59% and a complete removal of the target compound were achieved.