A facile single-pot synthesis of visible-light-driven AgBr/Ag2CO3 composite as efficient photocatalytic material for water purification

Immobilization of photocatalytic materials for (waste)water treatment using 3D printing technology - advances and challenges

Photocatalysis has been considered a promising technology for the elimination of a wide range of pollutants in water. Various types of photocatalysts (i.e., homojunction, heterojunction, dual Z-scheme photocatalyst) have been developed in recent years to address the drawbacks of conventional photocatalysts, such as the large energy band gap and rapid recombination rate of photogenerated electrons and holes. However, there are still challenges in the design of photocatalytic reactors that limit their wider application for real (waste)water treatment, such as difficulties in their recovery and reuse from treated (waste)waters. 3D printing technologies have been introduced very recently for the immobilization of materials in novel photocatalytic reactor designs. The present review aims to summarize and discuss the advances and challenges in the application of various 3D printing technologies (i.e., stereolithography, inkjet printing, and direct ink writing) for the fabrication of stable photocatalytic materials for (waste)water treatment purposes. Furthermore, the limitations in the implementation of these technologies to design future generations of photocatalytic reactors have been critically discussed, and recommendations for future studies have been presented.

Boosting the photocatalytic properties of NaTaO3 by coupling with AgBr

AgBr/NaTaO3 composites, with different molar % of NaTaO3 (Br/NTO(X%)), have been synthesized by simple precipitation methods; bare NaTaO3 was synthesized by hydrothermal procedure, while AgBr was synthesized by a precipitation procedure using cetyl-tri-methyl-ammonium bromide (CTAB) and AgNO3. Samples have been characterized by X-ray diffraction (XRD), N2 adsorption, UV–vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of the as-prepared photo-catalysts was evaluated through photocatalytic degradation of rhodamine B (RhB), methyl orange (MO) and caffeic acid (CAFA) under UV and visible illumination. Single AgBr material and Br/NTO(X%) composites displayed the ability to absorb light in the visible region, while NaTaO3 is only photoactive under UV irradiation. Based on the position of conduction and valence bands of AgBr and NaTaO3, the heterojunction between these two photo-catalysts corresponds to a type II junction. In the case of photocatalytic degradation of RhB and CAFA, Br/NTO(x%) composites have highest photocatalytic activity than that obtained by both parental materials under the same operational conditions. AgBr and Br/NTO(x%) composites achieve a fast degradation of MO, together with a considerable adsorption capacity, attributed to the presence of a remaining amount of residual CTAB on the AgBr surface. In summary, coupling AgBr with NaTaO3 improves the photocatalytic activity under both UV and visible illumination with respect to the parental components, but the performance of the composites is highly dependent on the type of substrate to be degraded and the illumination conditions.

Preparation of Ag3PO4/CoWO4 S-scheme heterojunction and study on sonocatalytic degradation of tetracycline

In this study, 0.6Ag₃PO₄/CoWO₄ composites were synthesized by hydrothermal method. The prepared materials were systematically characterized by techniques of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), N₂ adsorption/desorption, and UV-vis diffuse reflectance spectrum (DRS). Furthermore, the sonocatalytic degradation performance of 0.6Ag₃PO₄/CoWO₄ composites towards tetracycline (TC) was investigated under ultrasonic radiation. The results showed that, combined with potassium persulfate (K₂S₂O₈), the 0.6Ag₃PO₄/CoWO₄ composites achieved a high sonocatalytic degradation efficiency of 97.89 % within 10 min, which was much better than bare Ag₃PO₄ or CoWO₄. By measuring the electrochemical properties, it was proposed that the degradation mechanism of 0.6Ag₃PO₄/CoWO₄ is the formation of S-scheme heterojunction, which increases the separation efficiency of electron-hole pairs (e^--h⁺) and generates more electrons and holes, thereby enhancing the degradation activity. The scavenger experiments confirmed that hole (h⁺) was the primary active substance in degrading TC, and free radicals (OH) and superoxide anion radical (O₂^-) were auxiliary active substances. The results indicated that 0.6Ag₃PO₄/CoWO₄ nanocomposites could be used as an efficient and reliable sonocatalyst for wastewater treatment.

Revealing the charge transfer mechanism in magnetically recyclable ternary g-C3N4/BiOBr/Fe3O4 nanocomposite for efficient photocatalytic degradation of tetracycline antibiotics

Pharmaceutical compounds in water bodies pose hazards to the ecosystem because of their biotoxicity potency. To eradicate such pharmaceutical compounds, a novel g-CN/BiOBr/Fe₃O₄ nanocomposites was prepared using a simplistic route and appraised for photodegradation of model tetracycline antibiotics. The g-CN/BiOBr/Fe₃O₄ nanocomposites exhibited complete tetracycline degradation in just 60 min exposure of simulated light irradiation, which is 6 times higher than the g-CN. Under the analogous condition, the tetracycline mineralization ability of the g-CN/BiOBr/Fe₃O₄ nanocomposites was evaluated to be 78% of total organic carbon removal. The superior photocatalytic performance is ascribed to the extended visible light harvesting ability and enhanced charge carrier separation/transfer with impeded recombination rate in light of effective indirect Z-scheme heterojunction construction. Based on band-edge potential and radical trapping studies indicate that h⁺ > •O₂^- > •OH are the active species responsible for photodegradation. Furthermore, the ternary nanocomposites are magnetically retrievable and recyclable while retaining their stable photocatalytic performance. This work endows a new perspective on the rational design and construction of magnetically recoverable ternary nanocomposite for environmental remediation.

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.

Rational design of Ag2CO3-loaded SGO heterostructure with enhanced photocatalytic abatement of organic pollutants under visible light irradiation

The photocatalytic activity of semiconducting silver carbonate was restricted by the lower stability and fast recombination rate of photogenerated electron-hole pairs. Sulfur-doped graphene oxide (SGO) is used as a cocatalyst for improving the photocatalytic activity of Ag₂CO₃ by reducing the recombination rate. A simple precipitation method was used for the modification of silver carbonate. The chemical, physical, optical, and electrochemical properties of the modified photocatalyst was characterized by XRD, SEM, TEM, UV-vis DRS, XPS, CV, impedance, and amperometry. The fabricated SGO-Ag₂CO₃ composite was successfully degraded various organic pollutants such as methylene blue (MB), rhodamine B(RhB), methyl orange (MO), tartrazine, and thiram with augmented mineralization. The optimization of weight percentage of the developed binary composite with 0.5% SGO-Ag₂CO₃ showed enhanced photocatalytic degradation and followed pseudo-first-order kinetics with rate constant 0.126. More than 90% of degradation efficiency of the pollutants within a short time promises the binary heterostructure for future industrial applications. The excellent stability and reproducibility of the composite opened a new route in the treatment of wastewater.

Fabrication of novel AgVO3/BiOI nanocomposite photocatalyst with photoelectrochemical activity towards the degradation of Rhodamine B under visible light irradiation

In the present work, a visible light driven AgVO₃/BiOI nanocomposite photocatalyst with different wt % (1, 2, 3) of AgVO₃ was fabricated by using facile hydrothermal method. Further, the nanocomposite was characterized by FT-IR, XRD, SEM, TEM, EDS, UV-vis DRS, photoluminescence and photoelectrochemical studies. The structural characterization showed nanorods on nanosheet surface. Among different AgVO₃ loaded samples, the photocatalytic efficiency of 1 wt % AgVO₃/BiOI nanocomposite was found to be comparatively higher than the pure BiOI and AgVO₃. The photodegradation rate constant values of pure BiOI, AgVO₃ and 1, 2, 3 wt % AgVO₃/BiOI nanocomposites are 0.006, 0.0033, 0.0255, 0.01575, 0.0116 min^-1 respectively. This enhanced photocatalytic activity was due to the increasing visible light absorption ability and efficient separation of the charge carriers. Thereby, the 1 wt % AgVO₃/BiOI nanocomposite photocatalyst exhibited increased photodegradation activity, photostability and recyclability characteristics. The radical trapping experiment confirmed the role of OH and h⁺ in the photocatalytic degradation of RhB. Based on this, the probable mechanism of degradation of RhB under visible light irradiation has also been proposed. Hence, we believe it could be a promising material that can be employed for the photodegradation of organic pollutants present in wastewater.

Production of copper nanoparticles exhibiting various morphologies via pulsed laser ablation in different solvents and their catalytic activity for reduction of toxic nitroaromatic compounds

Comparative experiments were conducted to determine the effects of various solvents (i.e., deionized water, methanol, ethanol, 1-propanol, butanol, ethylene glycol, hexane, and acetonitrile) on the final compositions, morphologies, and catalytic activities of copper-based nanoparticles (NPs). The NPs were effectively synthesized by pulsed laser ablation (PLA) using a copper plate as the target. The obtained copper NPs were characterized utilizing various analytical techniques. It was established that the developed methodology allows for the production of NPs with different morphologies and compositions in a safe and simple manner. When laser ablation of a solid copper plate was performed in acetonitrile, the formation of copper(I) cyanide cubes was observed. On the other hand, in deionized water and methanol, spherical and rod-like particles of copper(I) and copper(II) oxide were detected, respectively. The catalytic activity of the prepared copper NPs in the reduction of aromatic nitro compounds, such as 4-nitrophenol and nitrobenzene, was also evaluated. A high k value was determined for the reduction over the copper(II) oxide NPs produced in methanol. Moreover, particles with graphitic carbon (GC) layers exhibited superior catalytic performance in the reduction of a hydrophobic substance, i.e., nitrobenzene, over the reduction of 4-nitrophenol. The enhanced catalytic activity of this catalyst may be due its unique surface morphology and the synergistic effects between the copper nanostructure and the GC layer. Lastly, a detailed reduction pathway mechanism for the catalytic reduction of 4-nitrophenol and nitrobenzene has been proposed.

Application of life cycle assessment for desalination: Progress, challenges and future directions

The sustainability performance of the desalination processes has received increasing attention in recent years. In this study, the current progress and future perspective of a life cycle assessment (LCA) of desalination technology in 62 previous studies have been reviewed for the period 2004-2019. It was found that the number of LCA studies related to seawater reverse osmosis has gained popularity compared to other types of desalination technologies. The review emphasized the application of LCA to desalination by means of research objective, scope of study, life stages, and impact assessment. Although previous LCA studies were conducted to assess the environmental performance of the desalination technology, little attention was given to evaluating the impact of other sustainability aspects (i.e., economic and social). The latter part of this study discusses the challenges, feasibility, and recommendations for future LCA studies on desalination technology. The integration of the LCA approach with other approaches allows a comprehensive assessment of the sustainability performance of desalination technology. Thus, the combined approaches should be explored in future studies to gain insight into the sensitivity and uncertainty of the data to make an assessment that can be useful in policy-making.

Synthesis of CoCrFeO4-chitosan beads sun-light-driven photocatalyst with well recycling for efficiently degrading high-concentration dyes

It is highly desired to develop an efficient large surface area CoCrFeO₄-based beads sun-light driven photocatalysts with excellent recycling features for degrading high-concentration dyes. Herein, a novel CoCrFeO₄ oxide nanoparticles have customarily been synthesized by the combination of three metals (Co, Cr and Fe) via co-precipitation method in aqueous solution and then millimeter-scale CoCrFeO₄ oxide chitosan-composite beads (CoCrFeO₄-CB) were prepared by incorporating the CoCrFeO₄ in chitosan polymer in basic medium, which makes the adsorbent easier to separate. The number of optimized nanocomposite beads used for the removal of high-concentration dyes displays 5-time photoactivity enhancement under sun-light irradiation compared to pristine CoCrFeO₄. Based on the fluorescence spectra related to the formed OH amounts, temperature-programmed desorption and electrochemical results, it is deduced that the unprecedented photocatalytic activities are mainly attributed to the large surface area, and enhanced charge separation from the chitosan as well as its promotion effects on O₂ activation. Influencing factors that effect the photocatalytic efficiency of dyes, such as catalyst dose, dyes concentration, time, and the light source was also studied. More importantly, after five catalytic cycles, no evident deactivation was observed, suggesting the satisfactory stability of the investigated photocatalyst. Also, large numbers of superoxides radicals form which is the main active species participate in the degradation of acid black were analyzed using a radical trapping experiment. It is expected that our work could render navigated information for steering toward the design and applications of the CoCrFeO₄-based photocatalyst with sun-light utilization for environmental remediation.