Degradation Of Organic Pollutants In Water Research Articles

TiO2-based photocatalysts from type-II to S-scheme heterojunction and their applications

Photocatalysis is a promising sustainable technology to remove organic pollution and convert solar energy into chemical energy. Titanium dioxide has drawn extensive attention in this field owing to its high activity under UV light, good chemical stability, large availability, low price and low toxicity. However, the poor quantum efficiency derived from fast electron/hole recombination, the limited utilization of sunlight, and a weak reducing ability still hinder its practical application. Among the modification strategies of TiO2 to enhance its performance, the construction of heterojunctions with other semiconductors is a powerful and versatile way to maximise the separation of photogenerated charge carriers and steer their transport toward enhanced efficiency and selectivity. Here, the research progress and current status of TiO2 modification are reviewed, focusing on heterojunctions. A rapid evolution of the understanding of the different charge transfer mechanisms is witnessed from traditional type II to the recently conceptualised S-scheme. Particular attention is paid to different synthetic approaches and interface engineering methods designed to improve and control the interfacial charge transfer, and several cases of TiO2 heterostructures with metal oxides, metal sulfides and carbon nitride are discussed. The application hotspots of TiO2-based photocatalysts are summarized, including hydrogen generation by water splitting, solar fuel production by CO2 conversion, and the degradation of organic water pollutants. Hints about less studied and emerging processes are also provided. Finally, the main issues and challenges related to the sustainability and scalability of photocatalytic technologies in view of their commercialization are highlighted, outlining future directions of development.

Preparation of MoS2/CdS/TNAs ternary composite structures and study of their photocatalytic properties

TiO2 has long been favored by researchers as a representative of semiconductor photocatalysts. Titanium dioxide nanotubes (TNAs) have a larger specific surface area, which makes them more valuable for the design of photocatalyst carriers. CdS is also a typical photocatalytic semiconductor material with a narrow bandwidth, which has a better performance in the visible light region. However, it also has certain problems such as photocorrosion. The composite MoS2 has a better inhibition effect. In this study, MoS2 and CdS were composited on TNAs using electrochemical deposition for the first time, and MoS2/CdS/TNAs (MCT) ternary composite nanostructures were successfully prepared. The effects of electrochemical deposition voltage, reaction time, and the ratios of molybdenum and sulfur sources in the electrolyte on the MCT composite structures were investigated. In this work, the photocatalytic degradation of organic water pollutants was simulated using methylene blue, and the degradation rate reached 93.1% at 150 min. After cycling the degradation experiments for five times, the photocatalysts still had good stability. The results showed that the MCT has good photocatalytic activity, which provides a feasible way for TNAs in the design of photocatalyst carriers.

Fast microwave synthesis of WO2.9–W18O49/carbon particles for near infrared-driven photocatalytic water remediation

Photocatalytic water remediation is gaining much attention as a cost-efficient and environmentally friendly technology. We designed WO2.9–W18O49/carbon composite particles to overcome the drawbacks of semiconductor-based photocatalysts by extending light absorption capacity to the near-infrared region and achieving efficient charge separation. A 2.45 GHz microwave plasma successfully upgraded commercially available WO3 and polystyrene powders to the composite particles through a fast reaction with the typical heating and cooling rates of 30 and 470 °C/s, respectively. The synthesized composite particles exhibited broad absorption in the UV–Vis-NIR range and outstanding electrical properties. Besides, excellent NIR-driven photocatalytic performance was demonstrated for the degradation of organic water pollutants (rhodamine B), with the WO2.9–W18O49 homojunction contributing to sufficient spatial charge separation, resulting in considerably enhanced degradation rates by more than two orders of magnitude.

Efficient Photocatalytic Degradation of Aqueous Atrazine over Graphene-Promoted g-C3N4 Nanosheets

Atrazine is a systemic herbicide widely used in weed control. In recent years, it has been largely detected in surface and groundwater in several locations all over the world. Photocatalysis is a green and sustainable technology with huge application prospects in pollution control and the degradation of organic water pollutants. In this work, photodegradation of aqueous atrazine was investigated over pristine graphitic carbon nitride (g-C3N4) synthesized via urea pyrolysis and graphene/g-C3N4 composite synthesized via the in situ growth method involving direct deposition of g-C3N4 nanosheets on the graphene surface. The obtained photocatalysts were characterized using transmission and scanning electron microscopy, Fourier-transformed infrared spectroscopy, UV-visible spectroscopy, photoluminescence spectroscopy, X-ray diffraction, and surface area measurements. It was demonstrated that the composite material exhibited remarkable photocatalytic properties for the efficient degradation of aqueous atrazine under visible light at ambient temperature. After 5 h of reaction, atrazine conversion reached 100% in the presence of graphene/g-C3N4 composite, while the pristine g-C3N4 allowed 40% conversion under the same conditions, thus demonstrating the positive effect of graphene on the photocatalytic activity of g-C3N4. Moreover, graphene/g-C3N4 was shown to keep its activity even when it was recycled five times, thus proving its stability and its potential to be used at the industrial scale.

Ag2O-adorned ZnO nanostructures: cooperative and sustainable nanomaterial system for effective reduction and mineralization of hazardous water pollutants

Organic water pollutants like nitroaromatics and synthetic dyes are causing serious threats to water. Ever-growing urban and industrial activities along with population explosion are rapidly contributing severe level of water contamination. Semiconducting nanomaterial-based photocatalysis has been proven to be an effective process for degradation of organic water pollutants. In the current study, visible light active Ag2O-adorned ZnO nanostructures were fabricated by a simple two-step hydrothermal method and the prepared nanostructures were utilized for the photocatalytic mineralization of rhodamine B (RhB) dye with visible light radiation. The catalytic potential of as-synthesized nanostructures was also investigated for the reduction of nitroaromatics (4-NP and 4-NA) and RhB dye in the presence of NaBH4. The Ag2O-adorned ZnO nanostructures prepared with 5% of silver nitrate denoted as ZnO/Ag2O (5%) demonstrated stupendous photomineralization activity against RhB dye as almost 100% degradation of RhB dye was achieved within 100min of reaction time at pH = 6. The kinetic study revealed that the degradation reaction followed the pseudo-first-order kinetics and the kinetic rate constant (k) of photodecolorization reaction for optimal catalyst was calculated to be 61.4 × 10-3min-1. The nanostructures revealed excellent recyclability and photostability as 95% activity of the catalyst was preserved even after the fifth cyclic run. The catalytic reduction of the 4-NP, 4-NA, and RhB dye was completed in 21, 12, and 40min, respectively, in the presence of ZnO/Ag2O (5%) and NaBH4 solution. The kinetic rate constant values for the reduction reactions were determined to be 229.6 × 10-3, 454.2 × 10-3, and 105.5 × 10-3min-1 for 4-NP, 4-NA, and RhB dye, respectively. Thus, the obtained results suggest that the components of the prepared nanosystem help in mutually strengthening the catalytic and photocatalytic abilities of each other, indicating the development of a cooperative and sustainable nanomaterial system in the current study.

Application of nanocomposites in integrated photocatalytic techniques for water pollution remediation

In recent years, photocatalysis integrated with other water purification technique is emerging to decontaminate the polluted water effectively. Herein, a focus on adsorptive photocatalysis, photo-Fenton, photo–electrocatalysis, photocatalytic ozonation, sono-photocatalysis and photo–piezocatalytic techniques developed for degradation of organic water pollutants has been provided. Specifically, application of nanocomposites in the degradation of different organic pollutants (dyes, pesticides, antibiotics, phenolic compounds etc.,) via integrated photocatalysis was reviewed. The catalytic performances of different nanocomposites along with the experimental parameters such as dosage, light source, irradiation time, pollutant’ concentration was summarized. Photocatalysis integrated with multiple techniques was also introduced. Current challenges, future perspectives and conclusion of this literature survey have been briefed. Researchers who are working in photocatalytic water treatment might be benefited by this review.

Optimizing Co site electron structure by construction of heterogeneous interface for efficient sulfite activation on paracetamol removal

Sulfite(S(IV))-induced advanced oxidation processes (AOPs) have great prospect in the field of removing organic pollutants, yet developing highly efficient sulfite activation systems and optimizing active sites for favorable catalytic processes are important but still challenging. Herein, we have achieved a composite catalyst with modulated Co electron structure for efficient AOPs by decorating Co(OH)2 on ultrathin graphitic carbon nitride (g-C3N4) nanosheet through an adjustable strategy, which exhibits high catalytic performance in S(IV) activation system. At optimal pH 9, 92% of paracetamol (APAP) (0.005 mM) is removed with the degradation rate constant of k1 = 0.193 min−1 within 30 min in presence of the composite material. The in-situ synthesis mode introduces strong heterogeneous interface interaction, resulting in directional electron transfer from cobalt hydroxide layer to g-C3N4 sheet revealed by X-ray photoelectron spectroscopy and density functional theory (DFT) calculations. The underlying activity enhanced mechanisms for APAP in S(IV) activation system using Co(OH)2/g-C3N4 are proposed: (i) The ultrathin g-C3N4 nanosheets provide more anchoring centers for generating small Co(OH)2 nanoparticles with abundant active sites which benefit to form metastable intermediates of Co(II)-SO3; (ii) The strong interface interaction induces charge redistribution between Co(OH)2 and g-C3N4 conformed by DFT calculation, which modulates the d-band center of Co site and strengthens the bind of Co(II)-SO3, thereby giving rise to radicals (•OH, SO4• and O2•) and nonradicals (1O2 and electron transfer) oxidation for highly-efficient removal APAP. Our work will pave the way to build an environmentally friendly strategy for emerging organic pollutant degradation in water through building efficient catalysts in sulfite activation system.

Broad spectrum driven Y doped BiO2−x for enhanced degradation of tetracycline: Synergy between singlet oxygen and free radicals

The synergy of singlet oxygen and free radicals is crucial to driving organic pollutant degradation in water contain complex natural organic matter. In this study, the rare earth element yttrium doped bismuth oxide (Y-BiO2−x) photocatalyst was prepared by a hydrothermal method. Y doped BiO2−x enables produce oxygen vacancies and possess up-conversion property. The superoxide radicals (O2−), singlet oxygen (1O2), hydroxyl radicals (OH) and hole (h+) play a crucial role in photocatalytic reaction process. The increased 1O2 and hydrogen peroxide are mainly originated from O2−. The degradation efficiency of tetracycline (TC) reached 70.45 % and 40.17 % under Vis and NIR light, respectively. Notably, the TC removal efficiency of Y-BiO2−x maintained 65.92 % in the actual wastewater containing various anions and humic acid (HA), which originate from synergy of singlet oxygen and free radicals. This study provides a new strategy for synergistic singlet oxygen and free radicals to degradation of organic pollutants in complex water matrix.

Chemically fabricated ZnO/Ag/Ag Mo O /Zn Mo O heterojunction nanophotocatalysts for abating organic dyes in wastewater

Semiconductor photocatalytic technology is among the most promising technologies for degrading organic pollutants in wastewater. However, broadening the photocatalytic spectral-response region of the nanomaterial and tuning carrier behavior at heterojunction interfaces remain wastewater-treatment challenges. To address this issue, we fabricated ZnO/Ag/Ag m Mo n O l /Zn x Mo y O z (ZAAZ) heterojunction nanophotocatalysts through a simple one-step chemical reaction between active ZnO nanoparticles and Ag/Ag x H 3− x PMo 12 O 40 (Ag/AgPMo). The as-prepared ZAAZ heterojunction nanophotocatalysts were physically and chemically characterized, photocatalytic activity was evaluated, and the photogenerated carrier-transfer mechanism analyzed. The optimal nanophotocatalyst was highly crystalline and exhibited a bandgap and specific surface area of 3.06 eV and 13.9 m 2 g −1 , respectively; it photodegraded almost 100% of the initial Rhodamine B (RhB) concentration in 90 min under the optimized conditions, which is 3.7-times faster than ZnO nanoparticles. Furthermore, the ZAAZ heterojunction nanophotocatalyst delivered a photocurrent of 8.3 μA cm −2 , which is 31-times higher than that of its ZnO nanoparticle counterpart; it efficiently separated photogenerated carriers, transferred interfacial charges, and degraded 97% of the initial RhB concentration after three cycles of use, highlighting its excellent recyclability . These findings suggest that the developed heterojunction nanophotocatalyst is highly efficient for the photocatalytic degradation of organic water pollutants .

Green production of self-assembled silver nanoarrays on flexible substrate for direct detection and catalytic degradation of organic water pollutants

Facile eco-friendly green chemistry assisted (hybrid tea rose petals extract) self- assembled plasmonic silver nano structure arrays (AgNS) were fabricated on a flexible substrate. In-situ self-assembly during the reduction process lead to organize arrays like AgNS with smaller size Ag nanocubes. Synthetic mechanisms detailed with optimizations were deliberately projected with UV–visible absorption spectroscopic studies. Structural studies indicated the cubic system of silver with an average crystalline size of 20 nm. Electron microscopic images elucidate the array like self-assembled Ag cubes; outstand for high phase purity with 95.6% of Ag. As well, UV–vis absorption results confirmed the shape confinement of self-assembled Ag nanocubes with the SPR band located around 450–490 nm. Feasibility of AgNS array in catalytic degradation of Rhodamine B dye tests was assessed with efficient degradation of 97% within 8 min. Ever since AgNS were forthright in field of calorimetry detection, H2O2 calorimetry studies were portrayed. Further on, fabrication of flexible, cost-effective plastic SERS support as sensor was developed with AgNS array (GAFPS) is yet another milestone achieved in SERS sensor platform. Raman probe molecule (Rhodamine 6G (R6G)) was exploited in optimization experiments for SERS detection. The optimized GAFPS SERS sensor involved in detection of Methylene blue (MB) and Rhodamine B (RhB) dyes; Sensor sensitivity studies succeeded with its sensitivity limit down to nano-molar range for RhB whereas close to pico-molar range for MB. In nutshell, multifaceted features of self-assembled plasmonic AgNS brings in state of art in the detection and degradation of industrial waste water management systems.

Activation of peroxymonosulfate by MnFe2O4@BC composite for bisphenol A Degradation: The coexisting of free-radical and non-radical pathways

In this study, novel metallic oxide catalyst MnFe2O4@biochar composite was synthesized by sol–gel pyrolysis loading of MnFe2O4 on biochar, and then used to activate peroxymonosulfate (PMS) to degrade bisphenol A (BPA). Characterization results demonstrated that the Fe and Mn oxide particles were homogeneously distributed on the surface of biochar, which avoided the aggregation of metal oxides. The strong magnetism of the composite was conducive to recycling during practical application. In the PMS system activated by MnFe2O4@biochar composite, the removal rate and mineralization rate of 20 mg/L BPA reached 100% and 95.9% within 30 min, respectively. The quenching experiments and electron paramagnetic resonance (EPR) study verified the coexistence of free-radical and non-radical pathways in the MnFe2O4@biochar/PMS system, with O2•- as the dominant active species, followed by singlet oxygen (1O2). The catalytic degradation process could adapt a wide pH range from weak acid to the alkaline matrix and showed negligible influence by anions and humic acid. The characterization results confirmed the synergistic effect of the bimetal, proving that the introduction of biochar and second metal source into iron-based catalyst played an important role in the composite. Overall, the MnFe2O4@biochar showed promising performance in activating PMS for organic pollutant degradation in water with high stability and safe performance.

Halides and oxyhalides-based photocatalysts for abatement of organic water contaminants – An overview

Recently, halides (silver halides, AgX; perosvkite halides, ABX3) and oxyhalides (bismuth oxyhalides, BiOX) based nanomaterials are noticeable photocatalysts in the degradation of organic water pollutants. Therefore, we review the recent reports to explore improvement strategies adopted in AgX, ABX3 and BiOX (X = Cl, Br and I)-based photocatalysts in water pollution remediation. Herein, the photocatalytic degradation performances of each type of these photocatalysts were discussed. Strategies such as tailoring the morphology, crystallographic facet exposure, surface area, band structure, and creation of surface defects to improve photocatalytic activities of pure halides and BiOCl photocatalysts are emphasized. Other strategies like metal ion and/or non-metal doping and construction of composites, adopted in these photocatalysts were also reviewed. Furthermore, the way of production of active radicals by these photocatalysts under ultraviolet/visible light source is highlighted. The deciding factors such as structure of pollutant, light sources and other parameters on the photocatalytic performances of these materials were also explored. Based on this literature survey, the need of further research on AgX, ABX3 and BiOX-based photocatalysts were suggested. This review might be beneficial for researchers who are working in halides and oxyhalides-based photocatalysis for water treatment.

Waste preserved wood derived biochar catalyst for promoted peroxymonosulfate activation towards bisphenol A degradation with low metal ion release: The insight into the mechanisms

The rational disposal of waste preserved wood is of great significance since its embedded metals (Cu, As, and Cr) pose potential threat to environment and human health. In this study, a biochar catalyst derived from waste preserved wood (PWB) was prepared for the degradation of bisphenol A (BPA) via peroxymonosulfate (PMS) activation. The PWB exhibited prominent catalytic degradation capability towards BPA compared with common wood derived biochar (CWB). Further tests and analysis elucidated that both radical species (OH) and non-radical species (1O2) were generated by the PWB/PMS system, whereas only 1O2 was detected in CWB/PMS system. Specifically, the metal compounds, especially metallic Cu in the PWB activated PMS via radical pathway, and the CO groups in the biochar generated the non-radical pathway, the coexistence of which resulted in higher BPA degradation rate in PWB/PMS system. It was also demonstrated that the heavy metal ion leaching (As and Cr) in PWB/PMS system was negligible. Furthermore, the biochar could effectively inhibit the leakage of oxidized Cu ions. This study provides a novel approach to prepare high-efficient carbocatalysts for organic pollutant degradation in water, which also enables the waste preserved wood with an environmental nondestructive mode of dispatch.

Ferrous oxalate covered ZVI through ball-milling for enhanced catalytic oxidation of organic contaminants with persulfate

Zero-valent iron (ZVI), with high reduction capacity and cost effectiveness, has been widely used as an activator for persulfate in remediation of organic pollutants. However, the existence of inherent iron oxide shell blocked the transfer of proton and further reduced its reactivity. In present study, a novel persulfate (PS) activator BZVI@OA was synthesized via ball milling ZVI with oxalic acid dihydrate. Scanning electron microscope, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry and Time-of-flight secondary ion mass spectroscopy confirmed the original low proton conductive oxidation shell was replaced by a high proton conductive FeC2O4 shell. The generated shell significantly improved persulfate activated capacity, through which degradation rates of various contaminants were enhanced for 1.64 to 2.33 times. Dissolved oxalate was proved to form complexes with iron ions, dramatically reduced the potential difference and relieved the blocked cyclic conversion. Electron paramagnetic resonance and quenching experiments confirmed an inner sphere adsorption of PS on FeC2O4·2H2O shell which facilitated the peroxide bonds cleavage, leading high efficiency of ROS generation. The accelerated proton transition was confirmed with AC impedance method, resulting in fast and elevated surface bound Fe2+ for persulfate decomposition into active species. Furthermore, BZVI@OA/PS system demonstrated high tolerance over wide initial pH range and promising reusability within 6 cycles. This work clarifies an effective strategy for developing efficient modified ZVI as a PS activator for organic pollutant degradation in water.

Enhanced degradation of organic water pollutants by photocatalytic in-situ activation of sulfate based on Z-scheme g-C3N4/BiPO4

In recent years, the excellent performance of sulfate radical (SO4·−) in advanced oxidation process has attracted more and more attention. However, it requires the consumption of expensive persulphate (PMS/PDS), and the resulting sulfate ion (SO42−) requires subsequent processing procedures, which limits its practical application value. In this work, a Z-scheme heterojunction g-C3N4/BiPO4 (CNBx) photocatalyst was constructed to in-situ activate the residual SO42− , H2O and dissolved O2 in organic wastewater simultaneously and produce SO4·−, ·OH and O2·− efficiently, so as to realize enhanced organic pollutant treatment by using clean and renewable solar energy resources. Under the condition of 10 mM SO42− addition and 100 mW·cm−1 illumination, the degradation rate of BPA (C0 = 20 mg·L−1) by optimized CNB150 catalyst was 0.30 min−1, which was 50% higher than that without SO42− (0.20 min−1). Detailed characterizations shown that a direct Z-scheme heterojunction was formed between g-C3N4 and BiPO4, which could be simultaneously stimulated by light, and then effective charge separation and migration could be achieved through the internal electric field caused by the Fermi-level difference between the g-C3N4 (-0.12 eV) and BiPO4 (0.01 eV). In general, this study makes full use of renewable solar energy and provides a feasible path for promoting the simultaneous in-situ utilization of small molecules (SO42−, H2O and O2) that originally exist in water, which makes organic wastewater treatment more economic, eco-friendly and sustainable.

Solar light sensitive hybrid Ce4+/3+ doped perovskite magnesium zirconate nano cubes for photocatalytic hydrogen evolution and organic pollutant degradation in water

Dispersion of petite quantity (Mg1−xCexZryO3) of cerium dopant in the lattice of magnesium zirconate (MgZrO3) is an efficient strategy to stimulate solar light photocatalytic activity of the material and achieve superior charge carrier separation. In this research, we demonstrate the tailoring of MgZrO3 to become a solar light sensitive material for the degradation of methyl orange (MO) dye and hydrogen evolution from water. Cerium doped MgZrO3 nanocubes (Mg1−xCexZryO3NCs) showed 93% efficiency for the degradation of MO and was able to show a maximum hydrogen evolution rate of 13,318 µmol h−1 g−1. It was found that, concentration of cerium plays a key role in the overall performance of the photocatalyst. A systematic characterization by Brunauer–Emmett–Teller (BET), Scavenger experiments, Electron Spin Resonance Spectroscopy (ESR), Photoluminescence (PL) and photocurrent measurements of the Mg1−xCexZryO3 NCs showed that, it possesses high surface area, promotes transfer of photo-stimulated electrons and provides rich photo-active centers for the enhanced photocatalytic redox activity. Retention of structure and morphology even after rigorous cycling of the catalyst with respect to MO degradation and hydrogen evolution makes Mg1−xCexZryO3 NCs a robust photocatalytic material.

TiO2 Doped with Noble Metals as an Efficient Solution for the Photodegradation of Hazardous Organic Water Pollutants at Ambient Conditions

This work highlights new insights into the performance of TiO2 doped with noble metal catalysts for the photocatalytic degradation of organic water pollutants. Different samples of titanium dioxide doped with noble metals (Au and Pd) were successfully synthesized via incipient wet impregnation (IWI) and ultrasound-assisted impregnation (US) methods. X-ray diffraction, scanning electron microscopy and UV-Vis reflectance spectroscopy were used for the characterization of the obtained materials. Their photocatalytic efficiency was investigated in aqueous suspension thorough a series of laboratory tests performed under ultraviolet (UV-A) irradiation conditions using 2,4 dinitrophenol (2,4 DNP) as a target molecule. The results clearly show that the method used for the catalyst synthesis affects its photocatalytic activity. It was found that the samples prepared by the IWI method exhibited high photocatalytic activity, and the removal rate obtained with TiO2-Pd/IWI was higher than that found for TiO2-Au/IWI. Furthermore, for the best catalyst, some extra photocatalytic experiments were conducted with rhodamine 6G (R6G), a highly stable molecule with a very different chemical structure to 2,4 DNP, in order to check the reactivity of this material. Moreover, the recycling experiments carried out with TiO2-Pd/IWI clearly demonstrated the high photocatalytic stability of this material for the degradation of 2,4 DNP. All of the collected data confirmed the interesting photocatalytic potential of the selected catalyst in the elimination of organic pollutants with no obvious change in its reactivity after four reaction cycles, which is very promising for promoting future applications in water depollution.

Smart ZnO decorated optimized engineering materials for water purification under natural sunlight

Developing and designing smart civil engineering materials for environmental depollution in our daily life is a major issue. ZnO nanostructures implemented onto civil engineering material surfaces by low cost hydrothermal growth could be one of the most promising solutions, and already showed a good water purification efficiency by photocatalysis under UV light. Nevertheless, there are two main factors to work out in order to simplify and intensify the photocatalyst production on engineering materials. The first one is the reduction of the growth time. The second one is the use of sunlight, which is the most abundant, clean, and renewable light source available. However, reducing the growth time might have an impact on the photocatalytic efficiency due to the surface/volume ratio modification. In this work, a short and efficient hydrothermal synthesis (2 h or 1 h 30 min vs 4 h) was used to grow ZnO nanostructures directly on non-conventional substrates such as tiling and concrete, demonstrating an excellent photocatalytic activity for organic pollutant degradation in water under natural sunlight, even during cloudy days. Decreasing the growth time showed no significant influence on tiling samples and even increased their photocatalytic efficiency until the optimal value obtained with a growth time of 2 h. A strong impact of the shorter growth time was observed on concrete samples, as reducing the growth time leads to complex ZnO nanosheet structures with a lower gap value (3.11 eV for 1 h 30 min against 3.17 eV for 4 h) due to a possible influence of the surface pH value and the complex chemical composition of concrete.

Oxidative degradation of aromatic N-compounds using cobalt containing montmorillonite-based catalysts

The goal of this work was the synthesis of a montmorillonite based catalyst for advanced oxidative degradation of organic water pollutants. Montmorillonite (Mt) –rich bentonite was acid-activated (MtA), and impregnated with cobalt (II) solution using the incipient wetness impregnation method. The impregnation was followed by heat treatment. Cobalt(II) ions were added in the quantities corresponding to 0.5 and 1.0 of the cation exchange capacity value. All samples were characterized by using chemical analysis, X-ray powder diffraction (XRPD), Electron paramagnetic resonance (EPR), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) coupled with Energy-dispersive X-ray spectroscopy (EDS), Transmission electron microscopy (TEM) and low temperature N2 physisorption. The incorporation of the cobalt in the impregnated samples and the development of porous structure in the acid-activated ones were confirmed. The montmorillonite (Mt) was used as a catalyst support, while the cobalt in its oxide form was responsible for the generation of sulfo-radicals from Oxone®. Two aromatic N-compounds were tested as model pollutants: diazo dye - Acid Orange 10 (AO10) and nicotine. It was found that the synthesized catalysts could be used for the degradation of both pollutants, although more efficiently in AO10 degradation. The acid activation, higher cobalt loading, and temperature were found to be beneficial for the degradation of AO10.

β-FeOOH catalyzed peroxymonosulfate for organic pollutant degradation in water: radical and non-radical mechanism

Iron-based catalysts as peroxymonosulfate (PMS) activator are commonly used to oxidize and degrade azo dye. However, there are still some issues such as low catalytic performance, relatively less reactive oxygen species and high metal iron dissolution. As such, a novel iron oxyhydroxide (FeOOHs) with four crystal form was synthesized and employed as efficient PMS activator for AO7 degradation in this study. It was found that the crystal form of catalyst had significant influence on its catalytic performance. β-FeOOH exhibited the best catalytic performance, owing to its smallest lattice size, maximum specific surface area and highest surface hydroxyl density. β-FeOOH/PMS system possessed a great high apparent reaction rate constant (1.3919 h−1), which was about 17, 3, 31, 20, 14, 49 and 23 times higher than that in β-FeOOH/persulfate(PS), Fe0/PMS, Fe0/PS, Fe2O3/PMS, Fe2O3/PS, Fe3O4/PMS and Fe3O4/PS system, respectively. More importantly, radical quenching tests and Electron spin resonance (ESR) analysis revealed that OH., SO4.−, O2.− and 1O2 were involved in the reaction process. The catalytic mechanism proposed that β-FeOOH had the effective electron transfer rate performance, and Fe3+ underwent a reduction to Fe2+ during the β-FeOOH/PMS catalytic oxidation process. Then, the regeneration of Fe2+ on the hydroxylated surface of FeOOH promoted the formation of FeOH+, which was crucial for PMS activation and reactive oxygen species (ROS) generation. The recyclability tests proved good stability and reusability of β-FeOOH. This study provides a kind of new understanding of peroxymonosulfate activation for environmental remediation and advances the study of iron-based oxyhydroxide in heterogeneous catalysis.