Organic Pollutants In Aqueous Solution Research Articles

Enhanced degradation of 2,4,6-trichlorophenol by activated peroxymonosulfate with sulfur doped copper manganese bimetallic oxides

• S-doped Cu-Mn bimetallic oxides (S-CuMnO) were successfully prepared. • 100% of 2,4,6-TCP (20 mg/L) was decomposed and 60% of TOC was removed by PMS activated with S-CuMnO. • SO 4 − , OH, O 2 − and 1 O 2 were responsible for the rapid degradation of 2,4,6-TCP. • Sulfur doping improved not only the catalytic activity of the catalyst but also its stability. In this study, the sulfur-doped copper-manganese bimetallic oxides (labelled as S-CuMnO) were successfully fabricated via a calcination under N 2 protection and used as a catalyst to activate peroxymonosulfate (PMS) for the degradation of 2,4,6-trichlorophenol (2,4,6-TCP). For comparison, sulfur-doped monometallic oxides including S-CuO and S-MnO and non-doped copper-manganese bimetallic oxides (CuMnO) were also synthesized through the same processes. Complete decomposition of 2,4,6-TCP (20 mg/L) and a high removal of total organic carbon (60%) were achieved within 30 min at 0.8 mM PMS, 0.07 g/L S-CuMnO and pH 7. S-CuMnO exhibited the highest catalytic activity among the tested catalysts, which may be attributed to the abundant Cu(I), increased specific surface area and superior electrical conductivity of S-CuMnO. The results of electron paramagnetic resonance (EPR) and radical scavenger tests testified that the reactive oxygen species (ROS) included SO 4 − , OH, O 2 − radicals and singlet oxygen ( 1 O 2 ), which were mainly responsible for the efficient removal of 2,4,6-TCP. In addition, it was found that the catalytic activity of the used S-CuMnO could be greatly enhanced by calcination again under N 2 protection. Furthermore, the intermediates involved in the degradation of 2,4,6-TCP were identified and the possible degradation pathways were further proposed. This work opens up new perspectives for designing highly efficient catalysts to decompose organic pollutants in aqueous solution.

Construction of a novel nitrogen- and oxygen-containing GO-based composite with specific adsorption selectivity

A novel graphene oxide (GO)-based composite, which was covalently functionalized by 1,3-bis(tris(hydroxymethyl)methylamino)propane (BTP), was first fabricated. The adsorption properties of GO-BTP composite toward some inorganic ions including rare earth elements and heavy metal ions, as well as some organic substances such as phenols and dyes were investigated. It can be found that the adsorption capacities of GO-BTP composite for La3+, Er3+, Cu2+, Pb2+, tert-butyl hydroquinone (TBHQ), m-nitrophenol (MNP), p-nitrophenol (PNP), alizarin red S (ARS) and neutral red (NR) were 0, 0.6, 6.32, 16.25, 27.28, 80.88, 101.69, 54.4 and 101.32 mg g−1, respectively. The morphologies and the compositions of GO-BTP composite, as well as the adsorption mechanism, were investigated by scanning electron microscopy, specific surface area analysis by Brunauer–Emmett–Teller method, Fourier transform-infrared spectroscopy, thermal gravimetric analysis, zeta potential measurements and X-ray photoelectron spectroscopy, respectively. The results indicated that the removal rates of GO-BTP composite were around 90% for PNP and 98% for NR even after 10 cycles of sequential adsorption-desorption tests. The GO-BTP composite can be considered as a promising adsorbent in the efficient adsorption of organic substances and the effective separation of mixtures of inorganic and organic pollutants in aqueous solutions.

Self-Assembled Nano-Fe3C Embedded in Reduced Graphene Oxide Aerogel with Efficient Fenton-Like Catalysis.

Aiming at the removal of refractory organic pollutants in aqueous solution, self-assembled nano-Fe3C embedded in reduced graphene oxide (nano-Fe3C@RGO) aerogel was prepared by hydrothermal synthesis and high temperature treatment, and characterized by SEM, HRTEM, pore size distribution, XRD, XPS and FTIR. The results showed that the aerogel was porous, and most of the Fe3C particles were less than 100 nm in size. They were evenly dispersed and embedded in the RGO aerogel. Furthermore, the mapping images confirmed that the elements of carbon, nitrogen and iron were homogeneously distributed. Moreover, the specific surface area of the aerogel was up to 324.770 m2/g and most of the pore sizes were between 5 and 10 nm. The formation of nano-Fe3C was identified by XRD pattern and HRTEM. Analysis of an XPS spectrum indicates that the nano-Fe3C was embedded in the graphene layer. The aerogel contained a large number of functional groups, including –NH2, –NH and –C=O, etc., which greatly strengthened the adsorption of organics. Finally, the Fenton-like catalytic degradation properties of the self-assembled nano-Fe3C@RGO aerogel were investigated by testing the removal of methyl orange from the aqueous solution. The results showed that the value of Ct/C0 decreased to 0.050 after 240 min, suggesting a high degradation rate was obtained. Meanwhile, the chemical reaction was verified in accordance with the first-order kinetic model, and the higher temperature was beneficial to the catalytic degradation. At the same time, methyl orange was degraded into small molecules by the hydroxyl and superoxide radicals generated during the reactions. Therefore, the self-assembled nano-Fe3C@RGO aerogel, as a novel Fenton-like catalyst, introduces a new approach in the field of treatment of refractory organic wastewater.

Construction of crystal defect sites in UiO-66 for adsorption of dimethyl phthalate and phthalic acid

The influence of constructed crystal defect sites in the metal-organic framework on the adsorptive removal of phthalic acid and dimethyl phthalate from aqueous solution has been investigated by etching UiO-66 with three monocarboxylic acids (MAs), including acetic acid (AA), trifluoroacetic acid (TFA) and trichloroacetic acid (TCA). The incomplete replacement of bridging ligands in UiO-66s by MAs, leading to the departure of partial ligands and metal clusters to create mesopores in metal organic frameworks, was determined by thermogravimetric analysis (TGA), nuclear magnetic resonance ( 1 H NMR) and N 2 adsorption-desorption. The results showed that mediate defect would increase the specific surface area and introduce mesopores to some extent, and the crystal structure was gradually destroyed as the excess concentration of MAs. Among UiO-66 samples, the UiO-66 etched by AA with concentration of 1.6 mol/L (UiO-66-1.6AA) had the highest specific surface area while the UiO-66-0.2TCA had the largest pore volume, which significantly enhanced the adsorption capacity for DMP and PA (18.05% up of PA and 41.59% up of DMP to UiO-66) respectively. The experimental data followed the pseudo-first-order kinetic and Langmuir model. In addition, regeneration study showed that the adsorption capacity of PA and DMP on UiO-66-0.2TCA and UiO-66-1.6AA can still remain over 83 and 90% after five cycles, respectively. The crystal defect sites introduction of mesopores by etching method would be an effective strategy to adsorptive removal of organic pollutants in aqueous solution. • UiO-66 was etched by acetic acid, trifluoroacetic acid and trichloroacetic acid. • Etching shaped hierarchical pore structure in UiO-66. • Defective sites had various influence on adsorption capacity of PA and DMP. • Etching method significantly enhanced adsorption for molecules of different sizes.

Visible-light-driven photoelectrocatalytic activation of chloride by nanoporous MoS2@BiVO4 photoanode for enhanced degradation of bisphenol A

The massive emission of bisphenol A (BPA) has imposed adverse effects on both ecosystems and human health. Herein, nanoporous MoS2@BiVO4 photoanodes were fabricated on fluorine-doped tin oxide (FTO) substrates for photoelectrocatalytic degradation of BPA. The photocurrent density of the optimized photoanode (MoS2-3@BiVO4) was 5.4 times as that of BiVO4 photoanode at 1.5 V vs. Ag/AgCl under visible light illumination, which was ascribed to the reduced recombination of photogenerated charge carriers of the well-designed hybrid structure. 10 ppm of BPA could be completely degraded in 75 min by MoS2-3@BiVO4 photoanode, with a bias of 1.5 V vs. Ag/AgCl and 100 mM of NaCl as the supporting electrolyte. The electron paramagnetic resonance (EPR) and free radicals scavenging experiments confirmed that chlorine oxide radical (•ClO) played a dominant role in the degradation of BPA. 14 intermediates were detected and identified during photoelectrocatalytic degradation of BPA by MoS2-3@BiVO4 photoanode and 3 pathways were proposed based on the above intermediates. The hybrid film exhibited high stability and reusability, and promising application potential in photoelectrocatalytic degradation of organic pollutants in aqueous solution.

Application of Central Composite Design to the Photo Fenton Degradation of Methyl Orange Azo Dye Using Fe-Activated Carbon Catalyst

Photo-fenton oxidation technique is one of the emerging oxidation processes explored in treatment of organic pollutants in aqueous solutions. This research is focused on utilization of Fe(II) loaded activated carbon and H2O2(aq) in a photofenton process to generate hydroxyl radicals that mineralize methyl orange dyes. Samples of activated carbon were treated with Fe(NO3)2(aq) and characterized using SEM, pHZPC, specific surface area and boehm’s titration. The degradation of methyl orange by the iron loaded activated carbon (Fe-Ac), via photo-Fenton process, was investigated in lab-scale defined by experimental design. Central composite design (CCD) was used to evaluate the effects of the five independent variables considered for the optimization of the oxidative process: time, FeAc dose, methyl orange concentration, pH and H2O2 concentrations. In the optimization, the correlation coefficients (R2 ) for the quadratic model was 0.9941. Optimum reaction conditions were obtained at pH = 3, catalyst dose = 0.1 mg/100ml, H2O2 = 0.62ml, methyl orange concentration = 5mg/l and time = 30 minutes.

Preparation and photocatalytic activities for decomposition of methylene blue of zeolitic imidazolate framework-8

In the present study, zeolitic imidazolate framework-8 (ZIF-8) is synthesized quickly in methanol solvent with the support of ultrasound, and application of photocatalyst for methylene blue (MB) decomposition reaction under UV radiation. The obtained ZIF-8 was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and UV-Vis diffuse reflectance spectra (DR-UV-Vis). The influence pH and kinetics of photocatalytic MB decomposition and reusability of ZIF-8, were also investigated. The results indicated that ZIF-8 could work effectively in the wide pH range from 4 to 12. When the initial pH of the solution increases to 12, the adsorption capacity and MB decomposition efficiency are both high. The MB decomposition on the ZIF-8 photocatalyst followed a pseudo-first-order kinetics model. The structural strength of ZIF-8 as well as the relatively high photocatalytic efficiency after reuse three times shows that ZIF-8 has good reusability and can be applied to treatment of organic pollutants in aqueous solution.

Ag/ZnO/PMMA Nanocomposites for Efficient Water Reuse.

This work attempts to produce photocatalytic surfaces for large-scale applications by depositing nanostructured coatings on polymeric substrates. ZnO/poly(methyl methacrylate) (PMMA) composites were prepared by low-temperature atomic layer deposition (ALD) of ZnO on PMMA substrates. In addition, to increase the photocatalytic and antibacterial activities of ZnO films, Ag nanoparticles were added on ZnO surfaces using plasma-enhanced ALD. The morphology, crystallinity, and chemical composition of the specimens were meticulously examined by scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses. The noteworthy photocatalytic activity of the nanocomposites was proved by the degradation of the following organic pollutants in aqueous solution: methylene blue, paracetamol, and sodium lauryl sulfate. The antibacterial properties of the samples were tested using Escherichia coli as a model organism. Moreover, the possible toxic effects of the specimens were checked by biological tests. The present results unambiguously indicate the Ag/ZnO/PMMA nanocomposite as a powerful tool for an advanced wastewater treatment technology.

Bio-Based Polyurethane Foams with Enriched Surfaces of Petroleum Catalyst Residues as Adsorbents of Organic Pollutants in Aqueous Solutions

In this study the surface of bio-based polyurethane foam was enriched with different contents of catalyst residue from the petroleum industry. The foams were prepared with different residue contents, 20, 50, and 80 wt% relative to the total mass of the polyols and were characterized by several techniques, with X-ray diffraction, X-ray fluorescence spectrometry, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, microtomography, Fourier transform infrared spectroscopy and thermogravimetric. To determine the removing process the effects of various operating parameters, pH of the solution (2–12), initial concentration of pesticides (5–50 mg L−1), contact time (15–1440 min), and amount of adsorbent (30–400 mg) were investigated in a batch adsorption technique. The specific surface area of the residue was determined by the BET method as up to 150 m2/g and mean pore diameter of 4.20 ± 0.42 nm (mesopore), which explains the excellent results of the materials in the adsorption process. The high adsorption capacity is probably due to the presence of highly concentrated catalyst residue on the foam surface. Trifluralin pesticide was removed in water using these polyurethane foams with 20.0 mg L−1 initial concentration of herbicide, 30.0 mg adsorbent mass of, 5.0 pH, and 25.0 °C temperature. The chemically prepared foams with 50 wt% residue (PURC50) have higher adsorption capacities (70%) and can be used to remove trifluralin from natural waters effectively. The efficiency of removing the herbicide increased to 83% with the use of 400.0 mg adsorbent mass. The adsorption efficiency of the pure catalyst residue reaches a maximum (95.3%). The established adsorption method was appropriate for adsorption of trifluralin in contaminated waters.

Catharanthus Roseus Leaf Extract Mediated Facile Green Synthesis of Copper Oxide Nanoparticles and Its Photocatalytic Activity

In this research study, the sustainable and eco-friendly green synthesis report on the use of plant extract alternate to chemicals was discussed. The Catharanthus roseus extract was used as a natural reagent to synthesize nanoparticles a brief discussion on the usage of plant extract were also summarized.Copper oxide nanoparticles (NPs) were successfully prepared using a simple way involving the combination reaction between copper nitrate and leaf extract. The synthesis under leaf extract response played an important role and led to the formation of copper oxide NPs of different size and shapes. The catalyst was characterized by XRD, FTIR, UV–Vis–DRS, PL, SEM with EDX and TEM analysis. The crystalline structure and phase identification was examined using XRD analysis, The XRD results revealed formation of pure phase without any post annealing. Formation of the metal oxygen bond of CuO nanoparticles was confirmed by Fourier transform infrared spectroscopy (FTIR). The surface morphology of the CuO nanoparticles depicted nanorods and the size difference depends upon the method of synthesis. EDX analysis confirmed the phase-purity of the as synthesized nanoparticles. UV-Vis DRS of the as obtained nanorods exhibited the absorbance in the visible region. Photocatalytic activities of the CuO nanoparticles were evaluated based on photodegradation of rose Bengal under UV light irradiation. The results suggested that the nanocatalyst CuO has potential applications as an efficient catalytic material with high efficiency for the photocatalytic degradation of organic pollutants in aqueous solution under UV light irradiation.

A review on hybrid techniques for the degradation of organic pollutants in aqueous environment.

The creation of the modern world requires many industrial sectors, however, sustainability needs to be considered while developing industries. In particular, organic pollutants generated by many of these industries contaminate the environment leading to health and other issues. Advanced oxidation processes (AOPs) have been introduced to remove organic pollutants present in wastewater. Sonolytic degradation of organic pollutants is considered as one of the AOPs, however, this process has its limitations. In order to overcome the limitations, hybrid techniques involving ultrasound and other AOPs have been developed. That is, ultrasound combined with heterogeneous AOPs (ultrasound/metal ions, ultrasound/metal oxides, and ultrasound/photocatalysis) and homogeneous AOPs (ultrasound/ozone, ultrasound/H2O2, and ultrasound/persulfate) for the degradation/mineralization of organic pollutants. This review highlights the advantages of using hybrid techniques involving ultrasound for the degradation of organic pollutants in aqueous solutions.

Efficiency of ozonation process with calcium peroxide in removing heavy metals (Pb, Cu, Zn, Ni, Cd) from aqueous solutions

Heavy metal ions have deadly effects on all forms of life, and through the disposal of industrial wastewater, they enter water resources and, eventually, the food chain. Advanced oxidation processes can remove hazardous and non-degradable organic pollutants in aqueous solutions. Variables examined were initial concentrations of calcium peroxide and heavy metals, contact time, pH, and ozonation rate. Maximum removal rate of heavy metals by ozonation with calcium peroxide under optimal conditions (contact time = 90 min, pH = 3, heavy metal concentration = 25 mg/L, calcium peroxide concentration = 0.025 mg/L and ozonation rate = 1 g/min) in synthetic and real samples were respectively 89.8% and 64.6% for Pb, 92.1% and 73.9% for Cu, 90.4% and 69.7% for Ni, 86.9% and 59.1% for Cd, and 93.4% and 78.8% for Zn. Maximum COD removal rates in synthetic and real samples were 88.1% and 69.9%, respectively. Removal rates of heavy metals and COD under optimal conditions on wastewater from the Isfahan electroplating industry and steel company were determined. The use of the ozonation process with calcium peroxide can be recommended as a good, coefficient method for the removal of heavy metals in wastewater treatment.

Adsorption performance of hydrophobic/hydrophilic silica aerogel for low concentration organic pollutant in aqueous solution

Abstract Hydrophobic silica aerogels (SiO2(AG)) was prepared via sol-gel and solvent exchange method under ambient pressure, which could be transformed to hydrophilic after heated under 500∘C. Heat treatment cannot change its structure. SiO2(AG) samples were the micro-porous structure formed by numerous fine particles and had high specific surface area, pore size and pore volume. The absorption performance of hydrophobic/hydrophilic SiO2(AG) on nitrobenzene, phenol and methylene blue (MB) showed that hydrophobic SiO2(AG) exhibited strong adsorption capacity on slightly soluble organic compounds, while hydrophilic SiO2(AG) was much more effective on adsorbing soluble compounds, which could be analyzed by the hydrophobic and hydrophilic interaction theory between the adsorbent and adsorbate.Hydrophobic/hydrophilic SiO2(AG) adsorption performance for MB is superior to that for phenol, which could be explained via the electrostatic interaction theory.

Sol-Gel Sonochemical Triton X-100 Templated Synthesis of Fe2O3/ZnO Nanocomposites Toward Developing Photocatalytic Degradation of Organic Pollutants

Abstract The existing work emphasizes mainly to advance the low surface features of zinc oxide (ZnO) by dispersion of Fe2O3 nanoparticles on the ZnO surface fabricated via a sol-gel route with Triton X-100 as a structure and capping agent to synthesis a novel series of Fe2O3/ZnO nanocomposites (NCs) with novel features assembling between the two nanoparticle materials. Fe2O3/ZnO is an effective semiconductor which has higher efficiency in the removal of numerous organic dyes and other pollutants. The NCs was characterized via HRTEM, XRD, FTIR, BET, RS and UV–Vis DRS. A photocatalytic performance of the fabricated Fe2O3/ZnO nanocomposites was estimated by continual degradation of the methylene blue dye (MB) as an organic pollutant in aqueous solution. The comparison between pure ZnO (NPs) and Fe2O3/ZnO (NCs) show advanced photocatalytic performance under both UV and sunlight irradiation. The impact of several parameters, for example, dopant contents, photocatalytic dosage, pH, chemical oxygen demand (COD) and point of zero charge (PZC) were evaluated and discussed. In addition, the protective species’ role was estimated via a radical scavenger route. The photo-degradation data shown that the Fe2O3/ZnO (10 wt%) semiconductor is the fit photocatalyst between the fabricated semiconductors for the methylene blue dye (MB) degradation. The intensity reduction peak of UV emission and the intensity increment of visible emission were led to the lessening in recombination between electrons and holes which are finally responsible for the maximum photocatalytic performance of Fe2O3/ZnO nanocomposites. The gained results confirmed that the dopant content is the major factor in photocatalytic degradation activity.

Three-year lifetime and regeneration of superoxide radicals on the surface of hybrid TiO2 materials exposed to air

The generation and stabilization of reactive oxygen species (ROS), including the superoxide radical anion (O2−), have a huge potential in environmental remediation and industrial chemical processes, but they still remain a challenge. Here, we elucidate the formation, stability and reactivity of superoxide radicals spontaneously produced on the surface of a hybrid TiO2-acetylacetonate material exposed to air. EPR spectra reveal an exceptional lifetime (up to three years, in air at room temperature) of the adsorbed O2−, which can also be easily regenerated after its decay.The performances of this material in the degradation of organic pollutants in aqueous solution without any light irradiation indicate a heterogeneous catalytic mechanism, mediated by superoxide radicals, with a synergistic homogeneous action of hydroxyl radicals (OH), which are released in solution, as detected by the EPR spin trapping method. The regeneration ability of the adsorbed superoxide radicals by simple exposure to air counteracts the partial instability in aqueous environment of the organic component of the hybrid structure allowing the catalyst reuse.These structural and functional features joined to the simple preparation route open a new perspective in the field of advanced oxidation processes for hybrid TiO2 materials.

Synthesis visible photocatalyst carbon/BiOI and its photocatalytic degradation activity

The carbon/BiOI composite photocatalysts were synthesis by hydrothermal reaction and characterized by various methods. The as-prepared photocatalysts were used to remove organic pollutants in aqueous solution under visible light irradiation. The C/BiOI samples demonstrated excellent photocatalytic performance for degradation of methyl orange (MO), which is about 4 times higher than that of BiOI. Furthermore, C/BiOI also displayed good stability after 5 cycles testing. Such superior performance was attributed to the enhanced absorption ability and increased separation of photogenerated electrons and holes.

Construction of magnetic bifunctional β-cyclodextrin nanocomposites for adsorption and degradation of persistent organic pollutants

Herein, we report a novel magnetic bifunctional β-cyclodextrin nanocomposite (Fe3O4@β-CD-CDI) based on metal coordination, which may be used for adsorption and degradation of persistent organic pollutants in aqueous solution. More importantly, N,N’-carbonyldiimidazole (CDI) functionalized β-CD ligand (β-CD-CDI) was assembled on the surface of Fe3O4 by Zn-N interaction. The results of kinetic and isothermal adsorption model investigation indicated that the adsorption rate and capacity of Fe3O4@β-CD-CDI were better than other materials, suggesting the effective accessibility of adsorption sites. We further confirmed that Fe3O4@β-CD-CDI can be used as heterogeneous catalyst to remove BPA through Fenton-like reaction in the presence of hydrogen peroxide (H2O2). Moreover, the material effectively alleviated the secondary pollution owing to the existence of β-CD inner cavity. This study indicated that the magnetic Fe3O4@β-CD-CDI material has great potential applications in wastewater purification containing persistent organic pollutants.

Heterogeneous Fenton Catalytic Removal of Organic Pollutant in Aqueous Solution by using Coal Gangue as a Catalyst

Background: Coal gangue was used as a catalyst in heterogeneous Fenton process for the degradation of azo dye and phenol. The influencing factors, such as solution pH gangue concentration and hydrogen peroxide dosage were investigated, and the reaction mechanism between coal gangue and hydrogen peroxide was also discussed. Methods: Experimental results showed that coal gangue has the ability to activate hydrogen peroxide to degrade environmental pollutants in aqueous solution. Under optimal conditions, after 60 minutes of treatment, more than 90.57% of reactive red dye was removed, and the removal efficiency of Chemical Oxygen Demand (COD) up to 72.83%. Results: Both hydroxyl radical and superoxide radical anion participated in the degradation of organic pollutant but hydroxyl radical predominated. Stability tests for coal gangue were also carried out via the continuous degradation experiment and ion leakage analysis. After five times continuous degradation, dye removal rate decreased slightly and the leached Fe was still at very low level (2.24-3.02 mg L-1). The results of Scanning Electron Microscope (SEM), energy dispersive X-Ray Spectrometer (EDS) and X-Ray Powder Diffraction (XRD) indicated that coal gangue catalyst is stable after five times continuous reuse. Conclusion: The progress in this research suggested that coal gangue is a potential nature catalyst for the efficient degradation of organic pollutant in water and wastewater via the Fenton reaction.

Hydrodynamic cavitation degradation of Rhodamine B assisted by Fe3+-doped TiO2: Mechanisms, geometric and operation parameters.

In this paper, a novel method, hydrodynamic cavitation (HC) combined with Fe3+-doped TiO2, for the degradation of organic pollutants in aqueous solution is reported. The venturi tubes with different geometric parameters (size, shape and half divergent angle) are designed to obtain a strong HC effect. The structure, morphology and chemical composition of prepared Fe3+-doped TiO2 as catalyst are characterized via using XRD, SEM, TEM, XPS, UV-vis DRS and PL methods. The effects of added TiO2 (heat-treated at different temperatures for different times) and Fe3+-doped TiO2 (with different mole ratios of Fe and Ti) on the HC catalytic degradation of RhB are discussed. The influences of operation parameters including inlet pressure, initial RhB concentration and operating temperature on the HC catalytic degradation of RhB are studied by Box-Behnken design (BBD) and response surface methodology (RSM). Under 3.0 bar inlet pressure for 10 mg/L initial concentration of RhB solution at 40 °C operating temperature in the presence of Fe3+-doped TiO2 with 0.05:1.00 M ratio of Fe and Ti, the best HC degradation ratio can be obtained (91.11%). Furthermore, a possible mechanism of HC degradation of organic pollutants in the presence of Fe3+-doped TiO2 is proposed. Perhaps, this study may provide a feasible method for a large-scale treatment of dye wastewater.

Synthesis of polyimide-modified carbon nanotubes as catalyst for organic pollutant degradation via production of singlet oxygen with peroxymonosulfate without light irradiation

Polyimide-modified carbon nanotubes (PI/CNTs) were synthesized via a solvent-free thermal method and used as a metal-free catalyst to activate peroxymonosulfate for organic contaminant degradation without light irradiation. The characterization results suggested that PI was loaded onto the surface of CNTs. The catalytic ability of the PI/CNTs was strongly correlated with the content of PI in the catalysts. The PI/CNTs (22% of PI) showed the highest catalytic efficiency for organic pollutant degradation at room temperature. The degradation efficiency of acid orange 7 (AO7) dye was significantly enhanced to 98.9% within 15 min, compared to the efficiency of 2.2% exhibited by pure PI. The radical quenching tests and electron paramagnetic resonance spectrometry proved that singlet oxygen, instead of hydroxyl radicals or sulfate radicals, played a dominant role during the catalytic oxidation of AO7. The influences of operation parameters including temperature and catalyst amount were investigated. The PI/CNTs metal-free catalyst exhibited high catalytic activity under a broad range of pH values. The recycling study of four repeated reactions demonstrated good stability of the PI/CNTs. This work provided a promising metal-free catalyst for degradation of organic pollutants in aqueous solutions, contributing to the development of green materials for sustainable remediation.