Organic Contaminants In Aqueous Solution Research Articles

Recent advances in water falling film reactor designs for the removal of organic pollutants by advanced oxidation processes: A review

Chemical wastewater from industrial and urban activities is a major environmental concern. Advanced oxidation processes (AOPs) have emerged as efficient techniques for the removal of persistent organic pollutants from wastewater. AOPs generate highly reactive hydroxyl radicals (•OH) that effectively degrade and mineralize a wide range of organic contaminants in aqueous solutions. Research is ongoing to find simple and efficient reactor designs for AOPs. Water falling film (WFF) reactor designs have been effectively utilized for the removal of various organic pollutants from wastewater. This review provides an overview of the development and application of WFF reactor designs for organic pollutants degradation by various AOPs. This work summarizes recent studies on treating organic pollutants, highlights current challenges in applying WFF reactors for water treatment using AOPs, and proposes future research directions. The review aims to guide researchers and stimulate further investigations into practical applications of WFF reactors in wastewater treatment.

Carbon-based nanomaterials mediated adsorption and photodegradation of typical organic contaminants in aqueous fulvic acid solution.

In this work, the formation of carbon-based nanomaterials-fulvic acid (CNMs-FA) composites and their capacities for the adsorption and photodegradation of typical organic contaminants in aqueous solutions were investigated. The results suggested that the formation of CNMs-FA composites was dominated by adsorbing FA on CNMs via the physisorption process, which fit the pseudo-first-order kinetic model and the Langmuir isotherm model. The formed CNMs-FA composites were characterized by using the Brunauer-Emmett-Teller, scanning electron microscopy, and infrared spectroscopy techniques and further applied for examining their effects on the adsorption and photodegradation of selected organic contaminants in aqueous solutions. The adsorption of organic contaminants on CNMs-FA composites is mainly involved in hydrogen bonding and electrostatic interactions between organic contaminants and FA species adhering to CNMs. In addition, the CNMs-FA composites are able to promote the photosensitive degradation of organic contaminants due to the photogenerated reactive species including ROS and CNMs-3FA* under sunlight irradiation. This study provided a deeper and more comprehensive understanding of the environmental behavior of CNMs in real natural surface water and clarified the underlying mechanisms.

Oxidative Degradation of Emerging Organic Contaminants in Aqueous Solution by High Valent Manganese and Iron

Oxidative Degradation of Emerging Organic Contaminants in Aqueous Solution by High Valent Manganese and Iron

Construction of Novel Metal-Free Graphene Oxide/Graphitic Carbon Nitride Nanohybrids: A 2D–2D Amalgamation for the Effective Dedyeing of Waste Water

In this present study, we have reported a novel metal-free graphene oxide/graphitic carbon nitride (GO/g-C3N4) 2D/2D hybrid heterojunction for the removal of hazardous organic contaminants in aqueous solution under visible light embellishment. The reported photocatalyst was prepared by the combined ultrasonic dispersion method and thoroughly investigated by several spectral and microscopic studies viz FT-IR, p-XRD, SEM with EDX, TEM, XPS Photoluminescence etc., The photocatalytic activity of GO/g-C3N4 nanohybrids much outperformed than pristine g-C3N4 sample in the photodegradation of Rhodamine B and crystal violet organic pollutants. The enhanced synergistic effect of GO/g-C3N4 is mainly due to the proficient separation of photogenerated electron–hole pairs and tuned band gap with unique morphology. The major active species was determined by radical quenching experimental results with employing different scavengers. In this article, designates that the metal-free hybrid hetrojunction photocatalyst was a hopeful material in the waste-water control.

A novel peroxymonosulfate activation process by periclase for efficient singlet oxygen-mediated degradation of organic pollutants

In this study, a novel peroxymonosulfate (PMS) activator, periclase (MgO) was applied to the activation of PMS for the degradation of organic contaminants in aqueous solution. It was found that MgO exerts an excellent and stable catalytic performance for PMS activation to degrade a wide range of pollutants including bisphenol A (BPA), phenol, chlorophenol, and dye, with degradation efficiencies of 100%, 100%, 41%, and 59%, respectively. Results from a combination of electron spin resonance (ESR), free radical quenching, chemical probe and isotope labeling investigations confirm that singlet oxygen (1O2) was the dominant reactive species generated in the PMS/MgO system and accounted for BPA degradation. The steady-state concentration of 1O2 was 13.2 × 10−13 M. Further evidence from X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FTIR) spectroscopy, and density functional theory (DFT) suggested that 1O2 was generated by the self-decomposition of PMS induced by surface hydroxyl groups on MgO. In addition, the degradation of BPA was hardly affected by anions and humic acid (HA) that commonly existed in the environmental matrices. The naturally occurring periclase also has high catalytic ability for PMS activation and BPA degradation. Compared with other transition metals-based radical pathways and carbonaceous materials-based non-radical pathways of PMS activation, MgO exerts a comparable catalytic performance but less potential risk and cheaper. This study developed a novel environmentally friendly catalyst with low cost and high efficiency for the selective degradation of organic pollutants in wastewater treatment.

Effect of Cr doping in CeO2 nanostructures on photocatalysis and H2O2 assisted methylene blue dye degradation

Optimization of Advanced Oxidation Processes (AOPs) is key for the demand in green and sustainable method for degradation of organic contaminants in aqueous solution. In this study, the effect of Cr doping on CeO2 nanostructure was investigated to evaluate the catalytic performances of the Cr doped CeO2 nanocomposites with Methylene Blue (MB) used as model contaminant. Two types of AOPs were also explored; photocatalysis and H2O2 assisted. The Cr-doped CeO2 samples were prepared by deposition precipitation method and characterized with XRD, FE-SEM-EDX, UV–vis Spectroscopy and TPR. Generally, increase in Cr doping improved the catalytic activity in MB degradation efficiency for photocatalysis and H2O2-assisted methods, where with 3% weight of Cr-doping achieved 41 % and 59 % of MB degradation across 100 min respectively. The improvement of catalytic activity was attributed to the effects on Cr doping, which lowers the CeO2 band gap and also the Cr species serving as electron trapping centers to slow down the recombination of the charge carriers. The MB degradation results also showed that for Cr-doped CeO2 system, H2O2-assisted was the more effective catalytic method compared to photocatalysis. Isopropanol has been found explicitly feasible to demonstrate a plausible scavenging properties toward hydroxyl radical by suppressing the MB degradation in the reaction media, thus, suggesting that, the MB degradation mechanism proceeds via hydroxyl radical species.

New insight into the mechanism of peroxymonosulfate activation by nanoscaled lead-based spinel for organic matters degradation: A singlet oxygen-dominated oxidation process

Crystalline iron-based nanoparticles with spinel structure have received great attention for catalyzing peroxymonosulfate (PMS). This study introduces lead ferrite (PbFe2O4) as a novel, simple, and efficient catalyst to activate PMS for the degradation of organic contaminants in aqueous solution. The results indicated that, under pH 9.0, nearly 100% of 10 μM thionine was removed in 20 min. Operation factors, including pH, oxidant concentrations, catalyst dosage, and coexisting ions, were investigated and found to be influential for the thionine removal. PbFe2O4 showed higher catalytic activity and lower ions leaching than well-crystallized lead oxide (PbO) and ferric oxide (Fe2O3). The results from the characterization of the PbFe2O4 with X-ray diffraction (XRD) before and after reaction suggested that the structure and properties of the catalyst kept stable, and the recovered catalyst exhibited good catalytic performance during the recycling batch experiments. Free radical quenching experiments and electron paramagnetic resonance (EPR) spectra revealed that singlet-oxygen (1O2) is the dominant active oxygen species rather than sulfate radical for thionine degradation in PbFe2O4/PMS system. Meanwhile, the possible pathways of 1O2 generation were proposed: the redox reaction between Pb(Ⅳ)/Pb(II) and PMS may play an key role in PMS activation. This study provides an interesting insight in PMS activation by the high-efficient non-radical process, and the PbFe2O4 could be as efficient and recyclable heterogeneous catalyst for organic degradation.

A review: Water pollution by heavy metal and organic pollutants: Brief review of sources, effects and progress on remediation with aquatic plants

Heavy metals and organic pollutants are ubiquitous environmental pollutants affecting the quality of soil, water and air. Over the past 5 decades, many strategies have been developed for the remediation of polluted water. Strategies involving aquatic plant use are preferable to conventional methods. In this study, an attempt was made to provide a brief review on recent progresses in research and practical applications of phytoremediation for water resources with the following objectives: (1) to discuss the toxicity of toxic chemicals pollution in water to plant, animals and human health (2) to summarise the physicochemical factors affecting removal of toxic chemicals such as heavy metals and organic contaminants in aqueous solutions by aquatic plants; (3) to summarise and compare the removal rates of heavy metals and organic contaminants in aqueous solutions by diverse aquatic plants; and (4) to summaries chemometric models for testing aquatic plant performance.

CuO-Co3O4@CeO2 as a heterogeneous catalyst for efficient degradation of 2,4-dichlorophenoxyacetic acid by peroxymonosulfate

CuO-Co3O4@CeO2 nanoparticles used as a heterogeneous catalyst were prepared via a sol-gel method and characterized by various techniques. For comparison, a series of oxides was investigated for activating peroxymonosulfate (PMS) during the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). The results indicated that CuO-Co3O4@CeO2 exhibited the highest catalytic performance among the catalysts. Complete degradation of 2,4-D (20 mg/L) was realized within 45 min at 1 mM PMS, CuO-Co3O4@CeO2 loading of 0.07 g/L, and pH of 6. Recycling experiments confirmed that CuO-Co3O4@CeO2 was very stable, and the 2,4-D degradation efficiencies ranged from 100% to 97.5%, decreasing by only 2.5% after the fifth run. The outstanding catalysis of CuO-Co3O4@CeO2 resulted from the synergy of cerium, cobalt, and copper. Electron paramagnetic resonance and radical scavenger experiments confirmed the production of SO4• − and •OH radicals in the CuO-Co3O4@CeO2/PMS system, which were responsible for efficient decomposition of 2,4-D. Furthermore, the combination of CuO-Co3O4@CeO2 andPMS was applied to treat natural water containing 2,4-D, and a high 2,4-D removal rate was also achieved. Based on these results, it was deduced that CuO-Co3O4@CeO2 can be utilized as a catalyst to activate PMS and destroy organic contaminants in aqueous solution.

Hydroxyapatite supported Co3O4 catalyst for enhanced degradation of organic contaminants in aqueous solution: Synergistic visible-light photo-catalysis and sulfate radical oxidation process

Through dispersing Co3O4 into a 3D flower-like OV-HAp (Oxygen Vacancies Hydroxyapatite) support, Co3O4@OV-HAp was facilely obtained and the agglomeration of Co3O4, as well as the leaching of Co2+ were efficiently inhibited. With both PMS (peroxymonosulfate) and visible-light presented, Co3O4@OV-HAp was used as a heterogeneous catalyst for model dye Rh B (Rhodamine B) degradation in which visible-light was introduced to be another activation source for ROSs (Reactive Oxygen Species) generation except for PMS. The catalytic reaction parameters were optimized and the concentrations of Co as well as the possible co-existent metal ions were all determined by ICP-OES (inductively coupled plasma optical emission spectrometer) and ICP-MS (inductively coupled plasma mass spectrometer) individually. The synergistic effect between visible-light photo-catalysis and SO4•- oxidation process greatly enhanced the catalytic activity of Co3O4@OV-HAp for Rh B degradation, and 100% Rh B can be degraded compared with only 5% by Co3O4. Moreover, the degradation rate was also greatly increased to about 212-fold higher in comparison with Co3O4.

Novel Photoelectrochemical Fuel Cell System Utilizing Titania Photocatalysts

In this work, one compartment Photoelectrochemical Cell (PEC) fabricated with inexpensive materials photodegraded selected organic compounds present in model waste waters, with the advantage of producing electrical current. Degradation of pollutants in waste waters by photoeletrocatalysis is well known. The photoelectrocatalytic degradation behaviour of the anti-inflammatory Sodium Diclofenac and others organic contaminants in aqueous solution was studied. TiO2 was utilized as the catalyst under different sources of UV and solar radiance. The catalyst was immobilized in a carbon cloth and in a variety of conductive supports as the photoanode and an air-cathode was utilized to allow an increase in oxygen concentration during the reduction process. By utilizing this photocatalytic process in a Photo Fuel Cell (PFC) device, the rate of organic pollutants destruction may be greatly enhanced, at the same time producing useful electrical energy. A range of environmental conditions will be explored such as fuel/pollutant concentration level, electrolyte composition and pH variation, in order to determine the best performing catalyst/support/environment combination. A transition metal oxide-based air cathode will also be used (replacing expensive platinum) in conjunction with a modified PFC design, thus characteristics and mechanistic insights will be ascertained as a result.

Degradation of organic pollutants by Vacuum-Ultraviolet (VUV): Kinetic model and efficiency

Vacuum-Ultraviolet (VUV), an efficient and green method to produce hydroxyl radical (•OH), is effective in degrading numerous organic contaminants in aqueous solution. Here, we proposed an effective and simple kinetic model to describe the degradation of organic pollutants in VUV system, by taking the •OH scavenging effects of formed organic intermediates as co-existing organic matter in whole. Using benzoic acid (BA) as a •OH probe, •OH was regarded vital for pollutant degradation in VUV system, and the thus developed model successfully predicted its degradation kinetics under different conditions. Effects of typical influencing factors such as BA concentrations and UV intensity were investigated quantitatively by the model. Temperature was found to be an important influencing factor in the VUV system, and the quantum yield of •OH showed a positive linear dependence on temperature. Impacts of humic acid (HA), alkalinity, chloride, and water matrices (realistic waters) on the oxidation efficiency were also examined. BA degradation was significantly inhibited by HA due to its scavenging of •OH, but was influenced much less by the alkalinity and chloride; high oxidation efficiency was still obtained in the realistic water. The degradation kinetics of three other typical micropollutants including bisphenol A (BPA), nitrobenzene (NB) and dimethyl phthalate (DMP), and the mixture of co-existing BA, BPA and DMP were further studied, and the developed model predicted the experimental data well, especially in realistic water. It is expected that this study will provide an effective approach to predict the degradation of organic micropollutants by the promising VUV system, and broaden the application of VUV system in water treatment.

Removal of Typical Organic Contaminants with a Recyclable Calcined Chitosan-Supported Layered Double Hydroxide Adsorbent: Kinetics and Equilibrium Isotherms

In this work, the calcined chitosan (CS)-supported layered double hydroxides were prepared, characterized, and further applied to remove organic contaminants in aqueous solution. The chitosan-supported layered double hydroxide calcined at 400 °C (CSLDO400) was found to be effective for the adsorption of azo dye and antibiotic. CSLDO400 showed excellent adsorption performance at a wide pH range from 5 to 9 for methyl orange (MO) while the adsorption of tetracycline (TC) was most efficient at a pH of 9, and the optimal CSLDO400 dosages were 0.175 g L–1 for MO and 0.375 g L–1 for TC. The divalent and trivalent anions have a great effect on removal efficiency of MO and TC, while the effect of monovalent anions adsorption can be neglected. The adsorption kinetics indicated that the MO and TC removal followed the pseudo-second-order model. In addition, it can be fitted well with both the Langmuir and Freundlich model for MO and TC at 298 K, respectively. The adsorptions of MO and TC on CSLDO400 were both sponta...

Enhanced Solar-Driven Applications of ZnO@Ag Patchy Nanoparticles

ZnO@Ag patchy nanostructures were demonstrated to be efficient and stable photocatalysts for the photodegradation of organic contaminants in aqueous solutions. The photoinduced charge transfer from the conduction band of ZnO toward the Fermi level of the noble metal was favored and exploited to enhance the photocatalytic efficiency of ZnO, with a mechanism based on hole stabilization. Naked ZnO and ZnO@Ag patchy nanostructures were demonstrated to degrade methylene blue, a model compound, in aqueous solution under 370–800 nm light irradiation (100 mW cm–2); in particular, the introduction of silver nanoparticles allowed one to increment twice the constant rate of the reaction when fitted as pseudo-first-order kinetics. Furthermore, the degradation of 2,4-dichlorophenol under direct sunlight irradiation was studied. The photo-oxidation catalyzed by patchy nanostructures was noticeably increased. In fact, the observed half time (t1/2) was reduced by almost 4 times in comparison with the value observed for b...

Normal and Inverse Diffusive Isotope Fractionation of Deuterated Toluene and Benzene in Aqueous Systems

Diffusive isotope fractionation of organic contaminants in aqueous solution is difficult to quantify, and only a few experimental data sets are available for compounds of environmental interest. In this study, we investigate diffusive fractionation of perdeuterated and nondeuterated benzene and toluene. Multitracer experiments were carried out in 1-D gel dissection tubes and in a quasi-2-D flow-through porous medium. The experiments allowed us to simultaneously and directly compare the diffusive and dispersive behavior of benzene and toluene. We observed an unexpected, opposite behavior of the two monoaromatic hydrocarbons. Toluene showed a normal diffusive isotope effect (DC7D8/DC7H8 = 0.96) with enrichment of the nondeuterated isotopologue in the direction of the diffusive and transverse dispersive fluxes. Conversely, the measured trends for benzene indicate inverse diffusive fractionation (DC6D6/DC6H6 = 1.02), with a remarkably faster diffusion rate of the perdeuterated isotopologue that was enriched i...

Comparison study on photocatalytic oxidation of pharmaceuticals by TiO2-Fe and TiO2-reduced graphene oxide nanocomposites immobilized on optical fibers

Incorporating reduced graphene oxide (rGO) or Fe3+ ions in TiO2 photocatalyst could enhance photocatalytic degradation of organic contaminants in aqueous solutions. This study characterized the photocatalytic activities of TiO2-Fe and TiO2-rGO nanocomposites immobilized on optical fibers synthesized by polymer assisted hydrothermal deposition method. The photocatalysts presented a mixture phase of anatase and rutile in the TiO2-rGO and TiO2-Fe nanocomposites. Doping Fe into TiO2 particles (2.40eV) could reduce more band gap energy than incorporating rGO (2.85eV), thereby enhancing utilization efficiency of visible light. Incorporating Fe and rGO in TiO2 decreased significantly the intensity of TiO2 photoluminescence signals and enhanced the separation rate of photo-induced charge carriers. Photocatalytic performance of the synthesized nanocomposites was measured by the degradation of three pharmaceuticals under UV and visible light irradiation, including carbamazepine, ibuprofen, and sulfamethoxazole. TiO2-rGO exhibited higher photocatalytic activity for the degradation of pharmaceuticals under UV irradiation, while TiO2-Fe demonstrated more suitable for visible light oxidation. The results suggested that the enhanced photocatalytic performance of TiO2-rGO could be attributed to reduced recombination rate of photoexcited electrons-hole pairs, but for TiO2-Fe nanocomposite, narrower band gap would contribute to increased photocatalytic activity.

Template-Free Synthesis of Monoclinic BiVO₄ with Porous Structure and Its High Photocatalytic Activity.

Monoclinic BiVO4 photocatalysts with porous structures were synthesized by a two-step approach without assistance of any templates. The as-prepared samples were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS), photocurrent responses, and electrochemical impedance spectra (EIS). It is found that the as-prepared BiVO4 samples had a porous structure with aperture diameter of 50–300 nm. Moreover, the BET specific surface area of the porous BiVO4-200 °C sample reaches up to 5.69 m2/g, which is much higher than that of the sample of BiVO4 particles without porous structure. Furthermore, a possible formation mechanism of BiVO4 with porous structure was proposed. With methylene blue (MB) as a model compound, the photocatalytic oxidation of organic contaminants in aqueous solution was investigated under visible light irradiation. It is found that the porous BiVO4-200 °C sample exhibits the best photocatalytic activity, and the photocatalytic rate constant is about three times of that of the sample of BiVO4 particles without porous structure. In addition, the photocurrent responses and electrochemical impedance spectra strongly support this conclusion.

Hierarchical carbon quantum dots/hydrogenated-γ-TaON heterojunctions for broad spectrum photocatalytic performance

There remains a pressing challenge in the efficient utilization of broad spectrum solar energy in the photocatalytic applications. Here we design and fabricate carbon quantum dots/hydrogenated-γ-TaON (CQDs/H-γ-TaON) hollow urchin heterojunctions that can enhance the UV–visible–NIR broad spectrum active photocatalytic property. Novel CQDs/H-γ-TaON photocatalysts have harnessed UV, visible, and near-infrared light to decompose organic contaminants in aqueous solution. Moreover, efficient photocatalytic hydrogen production as high as 496.5µmolh−1 with an apparent quantum efficiency of 12.2% under 420nm (about 61 times higher than that of conventional TaON) was achieved over CQDs/H-γ-TaON heterojunction, corresponding the order of hydrogen production rate: CQDs/H-γ-TaON>H-γ-TaON>γ-TaON. The improved UV and visible photocatalytic property can be attributed to high surface area from hollow nanostructures and efficient charge transfer based photoluminescence, electrochemical impedance and Mott–Schottky analysis. Especially, the NIR photocatalytic activity from the synergistic effects of the hydrogenation and the decoration of CQDs is ascribed to the efficient charge separation and transfer and up-converted photoluminescence property of CQDs that absorb NIR light and convert into visible light and transfer to visible-light photocatalytic H-γ-TaON. The CQDs/H-γ-TaON heterojunctions may open up more opportunities in the design of efficient broad spectrum active photocatalysts for environmental remediation and clean energy generation.

Synthesis and Characterization of Low-Cost Porous Carbon from Palm Oil Shell via K<sub>2</sub>CO<sub>3</sub> Chemical Activation Process

The abundant fraction of agricultural waste materials in the environment that poses disposal challenge could be converted into useful value added products such as activated carbon. Palm oil shell based carbon was prepared by two step process using K2CO3 as the chemical activant. The Langmuir surface area, BET surface area and pore volume were 817 m2/g, 707m2/g and 0.31cm3/g. From the FTIR analysis, carbonyls, alkenes and hydroxyls were identified. The SEM image shows gradual formation of pores due to elimination of volatiles and contaminants. Carbonization at 800°C for 2 hours and activation at same temperature for 1h has the highest yield of 23.27%. The proximate and ultimate analysis shows high percentage of carbon and low percentage of ash which is an indication of a good material for production of porous carbon. The activated carbon produced showed basic properties suitable for removal of organic contaminants in aqueous solutions. However, the aim of this study is to produce a green and porous carbon with controlled pores and surface properties for organic contaminants removal from water and wastewater.

A novel photocatalyst CeF3: facile fabrication and photocatalytic performance

The synthesized CeF3 nanoparticles can effectively decompose organic contaminants in aqueous solution and show high stability.