Organic Pollutants In Aqueous Solution Research Articles

Degradation of organic pollutants by the Cl-/PMS process.

The viewpoints on whether high concentrations of chloride ion (Cl-) promote or inhibit the oxidation activity of activated persulfates are still inconclusive. Furthermore, the degradation of organic pollutants by the persulfates in the presence of high Cl- concentrations without any activation medium has not yet been studied. In this work, the efficiency and mechanism of degradation of organic pollutants such as carbamazepine (CBZ), sulfadiazine (SDZ), and phenol (PN) by Cl--activated PMS (denoted as Cl-/PMS) were investigated. Results showed that Cl- could effectively activate PMS for the complete removal of CBZ, SDZ, and PN with reaction kinetic constants of 0.4516min-1, 0.01753min-1, and 0.06805min-1, respectively. Parameters such as PMS dose, Cl- concentration, solution pH, and initial concentrations of organic pollutants that affect the degradation efficiencies of the Cl-/PMS process were optimized. Unlike conventional activated persulfates, it was confirmed that the free chlorine was the main active species in the Cl-/PMS process. Finally, the degradation by-products of CBZ and SDZ as well as their toxicity were detected, and a possible degradation pathway for CBZ and SDZ was proposed. Though higher toxic chlorinated by-products were generated, the Cl-/PMS process was still an efficient oxidation method for the removal of organic pollutants in aqueous solutions which contain high concentrations of Cl-.

Visible light induced S-scheme charge transfer mechanism from Bi12TiO20 to CsPbBr3 for photodegradation of organic pollutants in aqueous solution

This work describes the formation of CsPbBr3/Bi12TiO20 S-scheme heterojunction photocatalysts using 3-mercaptopropionic acid (MPA) passivated CsPbBr3 nanocrystals (CPB) combined with Bi12TiO20 (BTO) nanorods. Under illumination, the charge carriers—undergo a process known as the S-scheme charge transfer, which significantly enhances their redox capability. The most efficient photodegradation of Rhodamine B (RhB) was recorded with the fine-tuned 10%CPB/BTO composite (degradation rate of 95.35% within 50 min, kapp = 0.06202 min−1). This improvement is primarily due to the MPA passivation, which increases the stability of the catalyst in aqueous solutions, and the S-scheme heterojunction design, which improves carrier separation and utilisation efficiency.

Microstructures, Optical, magnetic Properties, and photocatalytic activity of magnetically separable and reusable ZnO-Doped Fe3O4/rGO nanocomposite synthesized via green route

We report magnetically-separable, reusable, green-synthesized Fe3O4/rGO/ZnO, as heterogeneous catalyst for photo-Fenton degradation of organic pollutants in aqueous solution under certain treatments. Fe3O4 nanoparticles was green-synthesized using Moringa oleifera leaf extract, while rGO was synthesized utilizing Amaranthus viridis leaf extract. Fe3O4/rGO was composited under sonication treatment. Afterwards, Fe3O4/rGO was doped with ZnO with various concentration of ZnO. X-ray diffraction and selected area electron diffraction showed that Fe3O4 and ZnO had spinel cubic and hexagonal structure, respectively; another phase appeared as Fe2O3 spinel cubic structure. Crystallite size was decreased as the ZnO concentration increased. Morphology image showed almost spherical, non-uniform, and slightly dispersed particle under agglomerated condition, attaching to rGO sheets. The particle size of Fe3O4, Fe3O4/rGO, and Fe3O4/rGO/ZnO is 14.3; 14.1; and 10.4 nm, respectively. Fourier-transform infrared spectra showed metallic functional groups, such as Fe-O and Zn–O at 562–589 and 462–478 cm−1 also suggests nanocomposite formation. However, blue-shift absorption and band gap widening were observed with ZnO addition. Raman spectroscopy revealed the formation as-synthesized GO and rGO. Vibrating sample magnetometer showed that green-synthesized Fe3O4/rGO/ZnO exhibited superparamagnetic properties. Removal efficiency of photodegradation methylene blue was optimal for green-synthesized Fe3O4/rGO/ZnO under sonication treatment, reached 100 % degradation within 180 min for uptake every 30 min. Photodegradation was also analyzed using Langmuir-Hinshelwood kinetic model, resulting rate constant of 24.7 × 10−3 min−1 and half-life time of 28.1 min at optimum treatment. Reusability of photocatalytic activity after 3 cycles showed only a tiny drop in catalytic efficiency. Meanwhile, it possesses high stability in catalytic activity and structure. The green-synthesized Fe3O4/rGO/ZnO potential as an environmentally friendly reusable photocatalyst for wastewater degradation.

Cobalt etched graphite felt electrode for enhanced removal of organic pollutant in aqueous solution with a solid polymer electrolyte.

In this study, cobalt etched graphite felt electrodes were produced using a simple etching technique. It was used in combination with a solid polymer electrolyte (SPE) for the degradation of the target contaminant Orange II by Electro-Fenton (EF) technique in low conductivity water. In this method, 94% of Orange II in low conductivity water was removed in 90min. The characterization analysis substantiates the hypothesis that the electrodes produced exhibit a three-dimensional porous structure, augmented defect concentration, and enhanced electron transfer capability. In addition, the potential reaction mechanism was inferred from the radical quenching experiments, and hydroxyl radicals (·OH) were deemed the main reactive substances. The combination of cobalt etched graphite felt electrodes with SPE demonstrates remarkable efficacy in the treatment of organic wastewater characterized by low electrical conductivity.

True Order Determination of Sonochemical Degradation Kinetics of Organic Contaminants in Water Using the Half-lives Method

In the literature, the modeling of the sonolytic decomposition kinetics of organic contaminants in water has been carried out using the pseudo-first and pseudo-second order equations. The results obtained with this method are totally biased because it requires the assumption of the order of the degradation reaction, which is a real limitation, and the sonochemical oxidation mechanism is a very complex phenomenon that cannot be described by such simple models. In this paper, for the first time, the true order of the sonochemical degradation kinetics of organic pollutants in aqueous solutions at various initial substrate concentrations was determined using the half-lives method combined with the general rate law model, i.e., the pseudo-nth order equation. Linear and nonlinear regression techniques were used to determine the order of the sonolytic destruction reaction. The half-life technique for the general rate law model can adequately describe the experimental results of the sono-destruction of the investigated pollutants. For rhodamine B and naphthol blue black, the sono-destruction mechanism for both contaminants does not change as the initial contaminant concentration varies over the range examined, while for 4-isopropylphenol and furosemide, the sono-destruction mechanism changes as the initial substrate concentration varies. A fractional order of the sonolytic destruction reaction was determined for all the pollutants tested. These fractional orders of sono-destruction reactions indicate the complex nature and behavior of the reactions, often involving multiple steps or mechanisms. They also reveal a more complex interaction between pollutant concentration and sonolytic destruction rate. In a word, the method developed in this paper should be used to determine the real order of the sono-oxidation reaction of nonvolatile organic pollutants in aqueous phase.

Use of murici (Byrsonima crassifolia) and jabuticaba (Plinia cauliflora) residues in the preparation of porous materials: Effect of pH on the adsorption efficiency of the contaminants phenol, diethylphthalate and amoxicillin

Activated charcoals with the chemical activator (H3PO4) were synthesized from agro-industrial residues, Murici seeds (CA-MU) and Jabuticaba (CA-JA). The synthesized charcoals were characterized by thermogravimetric analysis (TG), N2 adsorption and desorption isotherms, Fourier transform infrared spectroscopy (FTIR), point of zero charge (pHPZC) and scanning electron microscopy (SEM). The charcoals produced presented mesoporous characteristics, surface areas of 884.226 m2.g−1 for CA-JA and 556.97 m2.g−1 for CA-MU, mean pore diameters suitable for adsorption of phenol (PHE), diethylphthalate (DEP) and amoxicillin (AMX). The chemical characterization indicated the acid profile of the surface of the charcoals, which presented pHPZC of 6.3 (CA-JA) and 6.7 (CA-MU). The adsorption studies, in aqueous solution of the pollutants (PHE), (DEP) and (AMX), indicated that the removal capacity is strongly influenced by the pH of the solution. Toxicity tests demonstrated that the adsorption process was responsible for decreasing the toxicity of the pollutants studied. Thus, given the results presented, the activated charcoals synthesized can be considered high potential adsorbents for applications in the removal of organic pollutants in aqueous solutions.

Preparation of Fenton Catalysts for Water Treatment

In the heterogeneous Fenton reaction, a solid catalyst reacts with H2O2 to generate highly oxidizing free radicals, that degrade organic pollutants in aqueous solutions. In this study, impregnation calcination was used to modify activated carbon and load it with various metal compounds. The synergistic catalysis of the various metal compounds showed improved catalytic activity, and the prepared heterogeneous Fenton catalyst exhibited high catalytic activity, a wide pH range, and good stability. The concentration ratios of the Fenton catalyst impregnation solutions-were as follows: Fe3+, Cu2+, Mn2+, and Ce3+ at 0.45, 0.72, 0.19, and 0.11 mol/L, respectively. The optimal sintering temperature of AC impregnation was determined through TGA/DSC, SEM, SEM-EDS, XPS, and XRD testing. At a final calcination temperature of 900 °C, the degradation efficiency of 10 ppm methylene blue reached 98.25% at pH 5 with 5 mM H2O2. After ten soaking cycles, the degradation efficiency exceeded 90%. The structure and performance of the catalysts were characterized using EPR, BET, ICP, and UV spectroscopy, demonstrating the excellent performance of the catalyst and providing an improved treatment plan for solving wastewater problems.

Photo-electrochemical degradation of rhodamine B using electrodeposited Mn3(PO4)2.3H2O thin films

Mn3(PO4)2·3H2O thin films have been grown using the cathodic electrodeposition method. The samples were characterized in terms of structural, morphological, optical and photo-electrochemical characteristics using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) combined with energy dispersive X-ray spectrometer (EDX), mott-Schottky and gap energy determination and electrochemical impedance spectroscopy (EIS), respectively. The photo-electrocatalytic performance of the resulting electrode has been performed towards the decomposition of rhodamine B (RhB). The achieved results have indicated that the decomposition attained was 95%, while the highest Chemical oxygen demand value was 79% after 25 min of reaction time, the efficiency of the operation was attributed to the creation of OH° and holes oxidizing species. The Mott-Schottky investigation has revealed the n-type conduction of Mn3(PO4)2·3H2O and EIS results are modelled to an equivalent circuit by using the Zview software consisting of a pair of resistors in parallel with a CPE. Moreover, the prepared thin films exhibit excellent stability for 4 cycles, rendering them a viable candidate for the decomposition of organic pollutants in aqueous solutions.

Bi-metalic ZIFs(Zn-M) (M: Co, Ni) for photocatalytic removal of organic pollutants in aqueous solutions

In this study, we successfully synthesised bi-metallic ZIF(Zn-M) of 2-methyl imidazole with a second metal (cobalt or nickel) binding to the ZIF network. All ZIF samples were synthesised at room temperature and characterised by using XRD, FT-IR, SEM, DRS, and nitrogen adsorption and desorption isotherms. The materials have high crystallinity with a large surface area. The materials’ photocatalytic ability was examined via the degradation of indigo carmine under a sun-light simulator. The second metal enhanced the photon harvesting ability of ZIF(Zn) because the materials can absorb photons in both UV and visible regions. Of the two catalysts, ZIF(Zn-Co) exhibited high photocatalytic ability when it removed 100% of indigo carmine from an aqueous solution. The catalyst adsorbed 45% of indigo carmine after 2 h and entirely degraded the remaining dye dring 1.5 h of solar irradiation. While Co2+ increased the catalyst’s surface area, Ni2+ reduced it, leading to lower photocatalytic efficiency.

The regulation of generation rate facilitates the win–win of ROS yield and utilization efficiency in heterogeneous persulfate catalytic oxidation system

Heterogeneous catalytic oxidation is one of the most effective methods to degrade various and complex organic pollutants in aqueous solution. Increasing reactive oxygen species (ROS) yield has always been the main objective to improve the oxidation efficiency. However, the mass production of ROS in a short time is inevitably faced with self-quenching and ineffective consumption. Herein, Cu-based composite oxides (CuOMOx) (M = Ca, Mg, Zn, Mn) were synthesized and used for catalytic activation of permonosulfate (PMS). Although the introduction of unreducible metal oxides significantly improved the activation efficiency of PMS, the abnormal phenomenon of lower substrate degradation efficiency and PMS stoichiometry appeared. The underlying mechanism is that the rapid production of ROS results in a mismatch of the production/effective consumption ratio, which causes massive ROS disappeared naturally before attacking the substrate. In this scenario, reasonable regulation of ROS generation rate by phosphate addition improved the utilization efficiency of ROS without affecting its yield. Our finding is beneficial to achieve a win–win situation of ROS yield and utilization efficiency in heterogeneous catalytic oxidation systems.

Encapsulation of phosphotungstic acid into UiO-66-(OH)2 for synergistic and rapid photocatalytic degradation of organic pollutants

PW12@ UiO-66-(OH)2 crystal was successfully fabricated by selecting UiO-66-(OH)2 as host matrix and encapsulating phosphotungstic acid (H3PW12O40, PW12) into its cage via one-pot synthesis. Characterization with FT-IR, PXRD, EDS and XPS confirmed that both the Keggin structure of PW12 and crystal structure of UiO-66-(OH)2 maintained well in the composite. The PW12@ UiO-66-(OH)2 can act as a photocatalyst to rapidly degrade organic pollutants in aqueous solution. UiO-66-(OH)2 was not only a carrier of PW12, but also an electron donor for the photocatalytic system. Due to the synergistic effect of PW12 and UiO-66-(OH)2, the degradation rate of methyl orange (MO) with PW12@ UiO-66-(OH)2 (90.42%) was greatly enhanced compared with using PW12 (28.25%) and UiO-66-(OH)2 (39.88%). Benefiting from the perfect size matching of PW12 and UiO-66-(OH)2, PW12@ UiO-66-(OH)2 exhibited satisfactory stability and reuse effect. This work will provide a new insight into the development of MOF-based composite photocatalysts to remove organic pollutants from wastewater.

Synthesis of Phosphotungstic acid/S-doped g-C3N4 Photocatalyst and Its Photocatalytic Degradation of Organic Pollutants in Aqueous Solutions

The S-doped g-C3N4 (SCN) was prepared by thermal condensation method using thiourea as a precursor, and then the phosphotungstic acid (PTA)/SCN composite photocatalytic material was prepared by reflux adsorption method. The photocatalytic degradation experiments of Rhodamine B showed that SCN20 had the highest photocatalytic degradation rate (74 %), which was 1.9 times and 3.5 times higher than that of PTA (39 %) and SCN (21 %), respectively. The photocatalytic degradation rate of SCN20 was increased by 5 times compared to that of SCN, indicating that the photocatalytic degradation performance of the composite material was significantly improved. The photocatalytic degradation mechanism study revealed that O2- was the main active species in the photocatalytic degradation of Rhodamine B, and the addition of PTA helped the effective separation of electrons-hole and improved the photocatalytic degradation rate. Our PTA/SCN is proposed as an environmental safety tool due to several advantages, such as low cost, convenient preparation, and efficient photocatalytic degradation of Rhodamine B.

Breaking interfacial charge transfer barrier by sulfite for efficient pollutants degradation: a case of BiVO4

Heterogeneous photocatalytic systems generally lack thermodynamic dependence on the degradation of organic pollutants in aqueous solution. Therefore, it is important to reveal the reasons for the inhibited surface kinetics but still be neglected. Herein, we reveal the mechanism that BiVO4 can’t degrade organics although it is thermodynamically feasible. The surface solvation and formation of double layer (compact layer and diffuse layer) makes low-polarity organics far away from the surface of BiVO4. We found that the introduction of sulfite can solve this problem. Theory calculation illustrates that sulfite can enter into the compact layer because of its higher adsorption energy on BiVO4 and lower adiabatic ionization potential (AIP). Then, photogenerated holes initiate the chain transformation of sulfite and produce strong oxidizing species which can diffuse out to degrade organics. This paper provides an insight into the understand the effects of solid-liquid interface on heterogeneously photocatalytic degradation of organic pollutants.

Electrochemical Oxidation of Organic Pollutants in Aqueous Solution Using a Ti4O7 Particle Anode.

Anodes based on substoichiometric titanium oxide (Ti4O7) are among the most effective for the anodic oxidation of organic pollutants in aqueous solutions. Such electrodes can be made in the form of semipermeable porous structures called reactive electrochemical membranes (REMs). Recent work has shown that REMs with large pore sizes (0.5-2 mm) are highly efficient (comparable or superior to boron-doped diamond (BDD) anodes) and can be used to oxidize a wide range of contaminants. In this work, for the first time, a Ti4O7 particle anode (with a granule size of 1-3 mm and forming pores of 0.2-1 mm) was used for the oxidation of benzoic, maleic and oxalic acids and hydroquinone in aqueous solutions with an initial COD of 600 mg/L. The results demonstrated that a high instantaneous current efficiency (ICE) of about 40% and a high removal degree of more than 99% can be achieved. The Ti4O7 anode showed good stability after 108 operating hours at 36 mA/cm2.

Activated carbon microspheres with high surface area for efficient organic contaminants removal

Modified carbon microspheres with large specific surface area (1334 m2 g−1) and abundant microporous structure are prepared using glucose as raw material via a simple hydrothermal and subsequent activation-carbonization process. The KHCO3 activation markedly increases the specific surface area (> 6 times) and pore volume (> 4 times) of obtained carbon microspheres, which endow it with excellent adsorption ability towards organic pollutants in aqueous solution. The KHCO3 activated carbon microspheres (KCMS) can efficiently remove 94 % methylene blue in 20 min (98 % in 60 min) at a low adsorbent dosage (10 mg adsorbent vs. 100 ml, 100 mg L−1 dye), and the saturation adsorption capacity reaches 1551.99 mg/g. The synergism of chemical interaction, pore filling effect, π-π interaction, hydrogen bond formation and electrostatic attraction gives KCMS excellent adsorption performance. The KCMS can be repeatedly used with high adsorption capacity. It also exhibits good adsorption ability towards rhodamine B (237.64 mg/g) and tetracycline (297.34 mg/g), indicating it is a wide range adsorbent. The results reveal that the activated carbon microspheres obtained by a simple process are efficient adsorbents for organic pollutants removal in wastewater. It suggests a new opportunity to develop novel low-cost adsorbent with excellent performance.

Investigation of the Effectiveness of Tetracycline Antibiotic Removal from Aqueous Solutions by Photo-Fenton Process using Biosynthesized Silver Nanoparticles

Introduction: Tetracycline is an antibiotic that is widely used around the world. Advanced oxidation processes are used for the degradation of resistant organic pollutants in aqueous solutions due to their high oxidation potential. This study aimed to estimate the performance of the ultraviolet rays/hydrogen peroxide/silver nanoparticles (UV/Ag/H2O2) in removing tetracycline antibiotics. Method: In this study, the degradation of tetracycline by the UV/Ag/H2O2 process was investigated under various conditions. The effects of different parameters, such as silver nanoparticles (1, 2, 4, and 6 mM), hydrogen peroxide concentration (10, 30, 50, 80, and 100 mM), pH (4, 7, and 10), and initial antibiotic concentration (15, 30, 45, and 60 mg/L) were investigated in the degradation of tetracycline. Finally, the antibacterial property of the synthesized nanoparticle was determined. Results: Under optimal conditions, within 90 min, the efficiency of tetracycline removal reached above 85% following pseudo-first-order kinetics. The obtained optimum conditions were as follows: tetracycline concentration (15 mg/L), oxidant concentration (80 mM), silver catalyst concentration (4 mM), and pH equal to 4. The size and morphological properties of nanoparticles were assessed by TEM, which showed that particles had a spherical shape with a diameter of about 1-50nm. The biosynthesized nanoparticle had high antibacterial properties. Conclusion: The results of this study showed that green synthesized silver nanoparticles with ultraviolet waves had great catalytic properties for oxidant activation and could also be used to inhibit and destroy resistant bacterial strains

Correction to “Electrocatalytic Oxidation Processes for Treatment of Halogenated Organic Pollutants in Aqueous Solution: A Critical Review”

Correction to “Electrocatalytic Oxidation Processes for Treatment of Halogenated Organic Pollutants in Aqueous Solution: A Critical Review”

Electrochemically Assisted Persulfate Oxidation of Organic Pollutants in Aqueous Solution: Influences, Mechanisms and Feasibility

Electrochemically (EC) assisted persulfate (PS) oxidation processes (EPOPs) have gained increasing attention in recent years. In this review, the current status and prospects of EC/PS degradation of organic pollutants are discussed and summarized. It was found that the oxidation of most organic contaminants could be significantly enhanced or accelerated using the combination of EC and PS compared to single treatments. Moreover, the effects of various operational variables on the removal of organic contaminants were investigated. Some variables are highly sensitive, and the optimal conditions are case-specific. Regarding the degradation mechanisms, radical-induced reactions and nonradical reactions both exist for the elimination of organic contaminants. Oxidants (including S2O82− and SO4•−) can be produced from SO42− near the anode, which is a unique feature of EPOPs. In some studies, the electrical energy consumption of EPOPs has been controlled to a reasonably low level in lab-scale attempts. Although there are still a few drawbacks or difficulties (e.g., potential electrode fouling, dependency on batch mode) for large-scale applications, EPOPs offer a promising alternative to traditional advanced oxidation techniques.

Efficiency enhancement of photocatalytic activity under UV and visible light irradiation using ZnO/Fe3O4 heteronanostructures

ZnO/Fe3O4 heteronanostructures (HNSs) have attracted great attention due to their possibility of removing organic pollutants in aqueous solutions, then detaching from aqueous solutions by magnetic fields. However, there is a lack of research on their photocatalytic performance under visible light irradiation and the mechanism for the degradation process is still arguable. We present here the enhancement in the photocatalytic activity of ZnO/Fe3O4 HNSs, synthesized by a facile hydrothermal technique, under both Ultraviolet (UV) and visible light irradiation. Particularly, the methylene blue (MB) degradation efficiency exhibited a great enhancement of up to 99.7% and 79.7% for HNSs with different ZnO:Fe3O4 mole ratios of 16:1 and 8:1 under UV and visible light, respectively. It could be explained by the transfer of electrons (i) from the conduction band (CB) of ZnO to that of Fe3O4 or/and (ii) from the CB of Fe3O4 to new defect states (e.g., Fe2+/Fe3+ levels) below the CB of ZnO. Additionally, ZnO/Fe3O4 HNSs show great stability in their photocatalytic activities when remained 95.1% and 92.1% after 5-reused cycles under UV and visible light irradiation, respectively. Therefore, the fabricated ZnO/Fe3O4 HNSs show great potential for enhancing the MB degradation efficiency under both UV and visible light.

Development of a TiO2/Sepiolite Photocatalyst for the Degradation of a Persistent Organic Pollutant in Aqueous Solution.

A clay-based TiO2 nanocomposite material was synthesized by a facile method, to investigate its structure and photocatalytic efficiency. The supported TiO2 nanoparticles were generated using a sol-gel method, and subsequently, mixed with a suspension of sepiolite. The material was recovered in powder form (Mc-80) and then calcined to properly arrange the crystal lattice of the TiO2 particles for use in heterogeneous photocatalysis (Mc-80-500). A powder X-ray diffractogram of Mc-80-500 revealed a dispersion of anatase and rutile phase TiO2 particles on the clay surface, exhibiting a size in the order of 4–8 nm. TEM images of Mc-80-500 confirmed the presence of isolated TiO2 beads on the surface of the fibrous sepiolite. The specific surface area of Mc-80-500 was larger than that of raw sepiolite and that of free TiO2 nanoparticles. Mc-80-500 was found to be more efficient in heterogeneous photocatalysis compared to other TiO2 materials based on sepiolite. Total depollution of a reactive dye (Orange G) was achieved after 1 h irradiation time, which is relatively quick compared to previous reports. The photocatalyst material can be washed with distilled water without chemical additives or calcination, and can be reused several times for photocatalysis, without loss of efficiency.