Unravelling the mechanistic role of Ti O C bonding bridge at titania/lignocellulosic biomass interface for Cr(VI) photoreduction under visible light

3D/3D Bamboo Charcoal/Bi2WO6 Bifunctional Photocatalyst for Degradation of Organic Pollutants and Efficient H2 Evolution Coupling with Furfuryl Alcohols Oxidation

Photocatalysis is one of the most promising pathways to relieve the environmental contamination caused by the rapid development of modern technology. In this work, we demonstrate a green manufacturing process for the 3D/3D rod-shaped bamboo charcoal/Bi2WO6 photocatalyst (210BC-BWO) by controlled carbonization temperature. A series of morphology characterization and properties investigations (XRD, SEM, UV-vis DRS, transient photocurrent response, N2 absorption-desorption isotherms) indicate a 210BC-BWO photocatalyst with higher charge separation efficiency, larger surface area, and better adsorption capacity. The excellent photocatalytic performance was evaluated by degrading rhodamine B (RhB) (98.5%), tetracycline hydrochloride (TC-HCl) (77.1%), and H2 evolution (2833 μmol·g-1·h-1) coupled with furfuryl alcohol oxidation (3097 μmol·g-1·h-1) under visible light irradiation. In addition, the possible mechanisms for degradation of organic pollutants, H2 evolution, and furfuryl alcohol oxidation were schematically investigated, which make it possible to exert photocatalysis by increasing the active radical. This study shows that the combination of bamboo charcoal and bismuth tungstate can be a powerful photocatalyst that rationally combines H2 evolution coupled with furfuryl alcohol oxidation and degradation of pollutants.

Graphite/carbon-doped TiO2 nanocomposite synthesized by ultrasound for the degradation of diclofenac

Graphite/C-doped TiO2 nanocomposite was synthesized at room temperature using a simple, impressive, and indirect sonication (20 kHz) by the cup horn system. Tetrabutyltitanate as the precursor of titanium and graphite (G) as the carbon source was used in the preparation of nanocomposite as a photocatalyst. The molar ratio of G/TiO2 as a key parameter was investigated in the synthesis of G/C-doped TiO2. The obtained materials were widely characterized using XRD, SEM, TEM, FTIR, XPS, and UV-Vis diffuse reflectance techniques. The UV-Vis diffuse reflectance spectroscopy results showed that the edge of light absorption of nanocomposite was distinctly red-shifted to the visible area via carbon doping. The XPS outcomes acknowledged the existence of the C, Ti, and O in the photocatalyst. The composite showed an enhancement in the dissociation efficiency of photoinduced charge carriers through the doping process. The photocatalytic activity of the synthesized nanocomposite was checked with diclofenac (DCF) as a pharmaceutical contaminant. The results displayed that G/C-doped TiO2 represented better photocatalytic performance for DCF than TiO2. This was due to the excellent crystallization, intense absorption of visible light, and the impressive separation of photoinduced charge carriers. Various active species such as •OH, •O2¯, h+, and H2O2 play a role in the degradation of DFC. Therefore, different scavengers were used and the role of each one in degradation was investigated. According to the obtained results, •O2¯ radical showed a major role in the photocatalytic process. This work not only proposes a deep insight into the photosensitization-like mechanism by using G-based materials but also develops new photocatalysts for the removal of emerging organic pollutants from waters using sunlight as available cheap energy.

Simultaneous preparation of ZnO/rGO composites through Zn(OH)2 decomposition and graphite oxide reduction and their photocatalytic properties

ZnO/reduced graphite oxide (rGO) composites were simultaneously prepared by the thermal reduction of graphite oxide (GO) and the decomposition of Zn(OH)2. The samples were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, photoluminescence, and DRS. Results indicate that Zn(OH)2 was heated and decomposed into ZnO at a low temperature (200 ℃), while GO was reduced to graphene. The synthesized ZnO particles were small and loaded on graphene layers. The ZnO/rGO photocatalysts exhibited excellent photocatalytic activity against methylene blue (MB) under simulated sunlight irradiation. The ZnO/50% rGO photocatalyst showed the best MB photodegradation rate of up to 99.7% within 3 min. Synchronous reaction provided an efficient, simple, and fast preparation method for ZnO/rGO composites, with an excellent solar photocatalytic degradation ability.

Fast g-C3N4 sonocoated activated carbon for enhanced solar photocatalytic oxidation of organic pollutants through Adsorb & Shuttle process

To solve low mass transfer in photocatalytic technology for water treatment, the combination of photoactive nanoparticles with highly adsorptive materials has been regarded as a successful approach. The optimization of photoactive particle coating in terms of dispersion on the surface of adsorbing support is the main key to reach a maximum synergism for pollutants removal. This study discusses the coating of as-prepared biomass based activated carbon by g-C3N4 using three routes, namely ball milling (AC-CN@BM), physical stirring (AC-CN@Phy) and ultrasonic assisted coating (AC-CN@US). The coating mechanisms by different processes were discussed using different characterization techniques. Ball milling based coating provides good g-C3N4 dispersion on the surface of AC, however, a partial degradation of g-C3N4 structure and a lower surface area were confirmed by FTIR, XRD and BET analysis. Physically designed sample shows a significant agglomeration of particles on the surface of AC. However, ultrasonic coating provides excellent distribution of g-C3N4 and high surface of the composite. In terms of photoactivity, AC-CN@BM exhibits the lowest adsorption and photocatalytic activity under solar light for the removal of ciprofloxacin. AC-CN@Phy showed medium performance, but less physical stability of g-C3N4 particles on AC, leading to their partial release. AC-CN@US showed the highest efficiency and stability after using; suggesting the good combination between g-C3N4 and AC, which in turn maximizes the removal of ciprofloxacin via Adsorb & shuttle process. The overall costs of composite, including the starting elements and the coating ultrasonic process are relatively low and green as compared to commonly reported routes.

High efficient COVID-19 waste co-pyrolysis char/TiO2 nanocomposite for photocatalytic reduction of Cr(VI) under visible light

Titanium dioxide (Titania) nanoparticle-coated biochar derived through co-pyrolysis of COVID-19 waste face mask (WFM) and Moringa oleifera seed cake (MO) provides an effective way to alleviate toxic metal in wastewater. This study investigates the effects of Biochar/titania photocatalyst preparation, characterization, and its photoreduction of Cr(VI). The morphological and functional modifications in the catalyst were identified using X-Ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, ultraviolet spectrophotometer, surface area analysis, and Raman spectrophotometer, respectively. The influencing parameters, namely, pH, photocatalyst dosage, initial pollutant concentration, and visible light irradiation time, have been investigated. The findings reveal that the Cr(VI) reduction by the photocatalyst was highly facilitated by photocatalytic process. The prepared photocatalyst shows higher and faster reduction rate of Cr(VI) and also improves the catalyst stability. The photoreduction of Cr(VI) ensembles well with pseudo-first order kinetics. At 180 min of reaction time, maximum Cr(VI) reduction of 98.65% was achieved at pH 2, 0.3 g/L catalyst dosage, and 10 ppm initial concentration, respectively. The synthesized photocatalyst shows excellent recycling performance up to 7 times, and these studies proved that the prepared catalyst is cost-effective and efficiently employed for removing pollutants.

2D/2D Biochar/Bi2WO6 Hybrid Nanosheets with Enhanced Visible-Light-Driven Photocatalytic Activities for Organic Pollutants Degradation

In this work, a novel two-dimensional/two-dimensional (2D/2D) hybrid photocatalyst consisting of Bi2WO6 (BWO) nanosheets and cotton fibers biochar (CFB) nanosheets was successfully prepared via a facile hydrothermal process. The as-prepared photocatalysts were characterized by a variety of techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. It was revealed that amorphous CFB nanosheets were uniformly immobilized on the surface of crystalline BWO nanosheets, and an intimate contact between CFB and BWO was constructed. The photocatalytic activities of the prepared BWO and CFB-BWO photocatalysts were evaluated by photocatalytic degradation of rhodamine B (RhB) and tetracycline hydrochloride (TC-HCl) in aqueous solutions under visible-light irradiation. Compared to the pristine BWO, the CFB-BWO composite photocatalysts exhibited significant enhancement in photocatalytic activities. Among all CFB-BWO samples, the 9CFB-BWO sample with the CFB mass ratio of 9% exhibited optimal photocatalytic activities for RhB or TC-HCl degradation, which was ca. 1.8 times or 2.4 times that of the pristine BWO, respectively. The improvement in photocatalytic activities of the CFB-BWO photocatalysts could be ascribed to the enhanced migration and separation of photogenerated charge carriers due to the formation of a 2D/2D interfacial heterostructure between CFB and BWO. Meanwhile, the possible mechanism of CFB-BWO for enhanced photocatalytic performance was also discussed. This work may provide a new approach to designing and developing novel BWO-based photocatalysts for the highly efficient removal of organic pollutants.

Conjugated Polymer Modifying TiO2 Performance for Visible-Light Photodegradation of Organics

Up to now, the use of TiO₂ has been considered a promising advanced technology for organic pollutants removal from air or water, since it has high biological and chemical stability, high photoactivity, low toxicity, and low-cost production. However, there are issues to be addressed in enhancing TiO₂ performance, and one of the current key issues is redesigning UV-active photocatalysts and making them active in the visible region of the electromagnetic spectrum. This way, solar light absorption will be insured, and thus, a more efficient photocatalyst could be obtained. For this reason, conjugated polymers and their derivatives are considered to act as photosensitizers, being able to shift the TiO₂ activity from the UV to the visible region. Therefore, this study focuses on the synthesis of TiO₂/conjugated polymer systems, which was accomplished by the deposition of poly-3,4-ethylene-dioxy-thiophene (PEDOT [-C₆H₄O₂S-]_n), a low-band semiconductor with an excellent stability due to its extending π-conjugated electron system, on titania nanoarchitecture. First of all, a TiO₂ nanoarchitecture was synthesized by an ultrasound-assisted sol-gel method. Then, TiO₂/PEDOT systems were obtained and characterized by using different techniques such as X-ray diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, UV-Vis diffuse reflectance, and N₂ sorption measurements. The synthesized composites confirmed their mesoporosity and lower band gap values compared to bare titania, which clearly shows the ability to work as photocatalysts under visible-light activity. Further, we demonstrated that an organic pollutant, Congo Red dye, used as a model molecule could be photodegraded with the synthesized TiO₂/PEDOT systems, with efficiencies of up to 95% in the case of T_convPEDOT under UV light and up to 99% for T_convPEDOT under visible-light irradiation, accomplishing in this way a successful synthesis of visible-light-activated titania photocatalyst.

Valorization of lignocellulosic biomass into sustainable materials for adsorption and photocatalytic applications in water and air remediation

An exponential rise in global pollution and industrialization has led to significant economic and environmental problems due to the insufficient application of green technology for the chemical industry and energy production. Nowadays, the scientific and environmental/industrial communities push to apply new sustainable ways and/or materials for energy/environmental applications through the so-called circular (bio)economy. One of today's hottest topics is primarily valorizing available lignocellulosic biomass wastes into valuable materials for energy or environmentally related applications. This review aims to discuss, from both the chemistry and mechanistic points of view, the recent finding reported on the valorization of biomass wastes into valuable carbon materials. The sorption mechanisms using carbon materials prepared from biomass wastes by emphasizing the relationship between the synthesis route or/and surface modification and the retention performance were discussed towards the removal of organic and heavy metal pollutants from water or air (NO_x, CO₂, VOCs, SO₂, and Hg⁰). Photocatalytic nanoparticle-coated biomass-based carbon materials have proved to be successful composites for water remediation. The review discusses and simplifies the most raised interfacial, photonic, and physical mechanisms that might take place on the surface of these composites under light irradiation. Finally, the review examines the economic benefits and circular bioeconomy and the challenges of transferring this technology to more comprehensive applications.

Solar light-based advanced oxidation processes for degradation of methylene blue dye using novel Zn-modified CeO2@biochar

Herein, a novel nanocomposite, namely, Zn-modified CeO₂@biochar (Zn/CeO₂@BC), is synthesized via facile one-step sol-precipitation to study its photocatalytic activity towards the removal of methylene blue dye. Firstly, Zn/Ce(OH)₄@biochar was precipitated by adding sodium hydroxide to cerium salt precursor; then, the composite was calcined in a muffle furnace to convert Ce(OH)₄ into CeO₂. The crystallite structure, topographical and morphological properties, chemical compositions, and specific surface area of the synthesized nanocomposite are characterized by XRD, SEM, TEM, XPS, EDS, and BET analysis. The nearly spherical Zn/CeO₂@BC nanocomposite has an average particle size of 27.05 nm and a specific surface area of 141.59 m²/g. All the tests showed the agglomeration of Zn nanoparticles over the CeO₂@biochar matrix. The synthesized nanocomposite showed remarkable photocatalytic activity towards removing methylene blue, an organic dye commonly found in industrial effluents. The kinetics and mechanism of Fenton-activated dye degradation were studied. The nanocomposite exhibited the highest degradation efficiency of 98.24% under direct solar irradiation of 90 min, at an optimum dosage of 0.2 g l^-1 catalyst and 10 ppm dye concentration, in the presence of 25% (V/V) 0.2 ml (4 µl/ml) hydrogen peroxide. The hydroxyl radical generated from H₂O₂ during the photo-Fenton reaction process was attributed to the nanocomposite's improved photodegradation performance. The degradation process followed pseudo-first-order kinetics having a rate constant (k) value of 0.0274 min^-1.

Conversion of novel tannery sludge-derived biochar/TiO2 nanocomposite for efficient removal of Cr (VI) under UV light: photocatalytic performance and mechanism insight

An investigation on the reduction of Cr (VI) pollutant from tannery effluents using TiO₂, SB/TiO₂, and c-SB/TiO₂ nano photocatalysts was presented in this study. For the preparation of Biochar-based TiO₂ photocatalyst (SB/TiO₂), tannery sludge was utilized as a precursor. Hydrothermal pre-treatment was adopted to prepare chemically activated SB/TiO₂ and SB/TiO₂ nanocomposites. The morphology, crystal structure, optical properties, and elemental composition of the prepared catalysts were analyzed by XRD, FT-IR, SEM-EDX, BET analysis, ZPC, PL, TGA, and Raman spectroscopy. The band gap analysis of Photocatalyst was measured using a DRS instrument, and band gap energy of 3.39 eV was obtained for c-SB/TiO₂ photocatalyst. The developed c-SB/TiO₂ catalyst exhibits a larger specific surface area of 646.85 m²/g than TiO₂ and SB/TiO₂ (74.58 m²/g and 573.74 m²/g), respectively. The enhanced photocatalytic activity for the pollutant removal was achieved by the photocatalyst due to their wide band gap and effective charge separation. The kinetic rate constant was achieved in the pseudo-first-order model, which fits well for the reduction of Cr (VI). Furthermore, at the optimal conditions of 10 mg/L contaminant concentration, pH 2, and 0.5 g/L catalyst dosage, 98.56% reduction was observed after 180 min of reaction. The OH acts as a major removal pathway for Cr (VI) contaminants with more than 50% reduction in COD. This study proves that c-SB/TiO₂ photocatalysts can remove toxic contaminants under UV light irradiation with good recycling performance up to 5 times.

Graphene oxide-incorporated silver-based photocatalysts for enhanced degradation of organic toxins: a review

Environmental contamination and scarcity of energy have been deepening over the last few decades. Heterogeneous photocatalysis plays a prominent role in environmental remediation. The failure of earlier metal oxide systems like pure TiO₂ and ZnO as stable visible-light photocatalysts demanded more stable catalysts with high photodegradation efficiency. Silver-based semiconductor materials gained popularity as visible-light-responsive photocatalysts with a narrow bandgap. But their large-scale usage in natural water bodies for organic contaminant removal is minimal. The factors like self-photocorrosion and their slight solubility in water have prevented the commercial use. Various efforts have been made to improve their photocatalytic activity. This review focuses on those studies in which silver-based semiconductor materials are integrated with carbonaceous graphene oxide (GO) and reduced graphene oxide (RGO). The decoration of Ag-based semiconductor components on graphene oxide having high-surface area results in binary composites with enhanced visible-light photocatalytic activity and stability. It is found that the introduction of new efficient materials further increases the effectiveness of the system. So binary and ternary composites of GO and Ag-based materials are reviewed in this paper.

Enhanced Photocatalytic Kinetics Using HDTMA Coated TiO2-Smectite Composite for the Oxidation of Diclofenac under Solar Light

Slow kinetics is one of the capital issues of photocatalytic technology because of its heterogeneous nature, which involves multi-step processes. Herein, we show that the simple modification of the sol-gel-based TiO2-smectite composite by hexadecyltrimethylammonium bromide (HDTMA) significantly boosts adsorption and photocatalytic efficient sol-gel-based light towards the removal of diclofenac from water. Three photocatalysts were prepared, including TiO2, TiO2-smectite, and HDTMA-TiO2-smectite. The materials were characterized to understand the surface interaction and crystal characteristics. In terms of photoactivity, it was found that the addition of HDTMA to TiO2-smectite improved the removal rate by twice. HDTMA changes the functional groups to TiO2-smectite composite allowing enhanced adsorption and photoactivity through the so-called Adsorb and Shuttle process. The recycling tests show that HDTMA-TiO2-smectite can be used up to four times with good performance. This modification approach could intensify the removal of pollutants from water instead of using complicated and costly techniques.

Heat and ZnCl2 chemical carbonization of date stone as an adsorbent: optimization of material fabrication parameters and adsorption studies

In the present study, the optimization of factors for the fabrication of highly adsorptive activated carbon from agricultural waste (date stone) was investigated by using ZnCl₂ as a chemical agent during the heat treatment. ZnCl₂ acts as a dehydration agent during the heat treatment, allowing a better porosity. In addition, it boosts the fragmentation of the lignocellulosic structure and the condensation of carbon rings. The findings of this investigation showed that the synthesis conditions for better ZnCl₂ chemical/heat carbonization to fabricate an adsorbent from date stone are 700 °C, 120 min, and 2.0 g/g. The characterization analysis showed that the as-prepared activated carbon exhibits a surface area of 1036 m²/g, an iodine number of 928.5 mg/g, and phenol number of 2.1 mmol/g, which are comparable to commercial activated carbons. Batch sorption tests to remove methylene blue (MB) from water showed a maximum adsorption capacity of 384.6 mg/g using the prepared activated carbon. Equilibrium data was best fitted by the Langmuir isotherm model. It was found also that the kinetic adsorption data obeyed the pseudo-first order, and both external diffusion and intra-particle diffusion control the adsorption. Based on the obtained results, the optimization of synthesis conditions may help the transfer of technology in terms of agriculture-based material valorization towards the environmental remediation.

A review of advances in multifunctional XTiO3 perovskite-type oxides as piezo-photocatalysts for environmental remediation and energy production

Over more than three decades, the field of engineering of photocatalytic materials with unique properties and enhanced performance has received a huge attention. In this regard, different classes of materials were fabricated and used for different photocatalytic applications. Among these materials, recently multifunctional XTiO₃ perovskites have drawn outstanding interest towards environmental remediation and energy conversion thanks to their unique structural, optical, physiochemical, electrical and thermal characteristics. XTiO₃ perovskites are able to initiate different surface catalytic reactions. Under ultrasonic vibration or heating, XTiO₃ perovskites can induce piezo-catalytic reactions due to the titling of their conduction and valence bands, resulting in the formation of separated charge carriers in the medium. In addition, under light irradiation, XTiO₃ perovskites are considered as a new class of photocatalysts for environmental and energy related applications. Herein, we addressed the recent advances on variously synthesized, doped and formulated XTiO₃ perovskite-type oxides showing piezo- and/or photocatalytic exploitation in environmental remediation and energy conversion. The control of structural crystallite size and phase, conductivity, morphology, oxygen vacancy control, doping agents and ratio has a significant role on the photocatalytic and piezocatalytic activities. The different piezo or/and photocatalytic processes mechanistic pathways towards varying applications were discussed. The current challenges facing these materials and future trends were addressed at the end of the review.

Recent Breakthroughs and Advancements in NOx and SOx Reduction Using Nanomaterials-Based Technologies: A State-of-the-Art Review

Nitrogen and sulpher oxides (NO_x, SO_x) have become a global issue in recent years due to the fastest industrialization and urbanization. Numerous techniques are used to treat the harmful exhaust emissions, including dry, traditional wet and hybrid wet-scrubbing techniques. However, several difficulties, including high-energy requirement, limited scrubbing-liquid regeneration, formation of secondary pollutants and low efficiency, limit their industrial utilization. Regardless, the hybrid wet-scrubbing technology is gaining popularity due to low-costs, less-energy consumption and high-efficiency removal of air pollutants. The removal/reduction of NO_x and SO_x from the atmosphere has been the subject of several reviews in recent years. The goal of this review article is to help scientists grasp the fundamental ideas and requirements before using it commercially. This review paper emphasizes the use of green and electron-rich donors, new breakthroughs, reducing GHG emissions, and improved NO_x and SO_x removal catalytic systems, including selective/non-catalytic reduction (SCR/SNCR) and other techniques (functionalization by magnetic nanoparticles; NP, etc.,). It also explains that various wet-scrubbing techniques, synthesis of solid iron-oxide such as magnetic (Fe₃O₄) NP are receiving more interest from researchers due to the wide range of its application in numerous fields. In addition, EDTA coating on Fe₃O₄ NP is widely used due to its high stability over a wide pH range and solid catalytic systems. As a result, the Fe₃O₄@EDTA-Fe catalyst is projected to be an optimal catalyst in terms of stability, synergistic efficiency, and reusability. Finally, this review paper discusses the current of a heterogeneous catalytic system for environmental remedies and sustainable approaches.

Sonoprocessing: From Concepts to Large-Scale Reactors

Intensification of ultrasonic processes for diversified applications, including environmental remediation, extractions, food processes, and synthesis of materials, has received attention from the scientific community and industry. The mechanistic pathways involved in intensification of ultrasonic processes that include the ultrasonic generation of cavitation bubbles, radical formation upon their collapse, and the possibility of fine-tuning operating parameters for specific applications are all well documented in the literature. However, the scale-up of ultrasonic processes with large-scale sonochemical reactors for industrial applications remains a challenge. In this context, this review provides a complete overview of the current understanding of the role of operating parameters and reactor configuration on the sonochemical processes. Experimental and theoretical techniques to characterize the intensity and distribution of cavitation activity within sonoreactors are compared. Classes of laboratory and large-scale sonoreactors are reviewed, highlighting recent advances in batch and flow-through reactors. Finally, examples of large-scale sonoprocessing applications have been reviewed, discussing the major scale-up and sustainability challenges.

Comparison of the photoactivity of several semiconductor oxides in floating aerogel and suspension systems towards the reduction of Cr(VI) under visible light

A massive amount of research has been done over the last three decades to develop photoactive materials which could be suitable for real-world use in water remediation sector. Water-floating photocatalysts could be one of the best options due to their technological characteristics in terms of efficiency and reasonability including a high oxygenation of the photocatalyst surface, a fully sunlight irradiation, easy recovery and reuse. In the present study, aerogel water-floating based materials were fabricated using poly(vinyl alcohol) and polyvinylidene fluoride as a polymer platform, and loaded with different semiconductors such as g-C₃N₄, MoO₃, Bi₂O₃, Fe₂O₃ or WO₃. The photocatalytic efficiencies of aerogel floating materials and the suspension of above-mentioned semiconductors were compared evaluating the photoreduction of Cr(VI) under visible light (λ > 420 nm). The results showed that Fe₂O₃ suspension was the most efficient but the slowest in floating system. On the contrary, g-C₃N₄ exhibited a good performance in suspension system, and on top of that it was very effective in floating system, wherein it ensures a total reduction of 10 ppm-Cr(VI) to Cr(III) within 20 min.

Recent advances in hybrid wet scrubbing techniques for NOx and SO2 removal: State of the art and future research

Recently, the discharge of flue gas has become a global issue due to the rapid development in industrial and anthropogenic activities. Various dry and wet treatment approaches including conventional and hybrid hybrid wet scrubbing have been employing to combat against these toxic exhaust emissions. However, certain issues i.e., large energy consumption, generation of secondary pollutants, low regeneration of scrubbing liquid and high efficieny are hindering their practical applications on industrial level. Despite this, the hybrid wet scrubbing technique (advanced oxidation, ionic-liquids and solid engineered interface hybrid materials based techniques) is gaining great attention because of its low installation costs, simultaneous removal of multi-air pollutants and low energy requirements. However, the lack of understanding about the basic principles and fundamental requirements are great hurdles for its commercial scale application, which is aim of this review article. This review article highlights the recent developments, minimization of GHG, sustainable improvements for the regeneration of used catalyst via green and electron rich donors. It explains, various hybrid wet scrubbing techniques can perform well under mild condition with possible improvements such as development of stable, heterogeneous catalysts, fast and in-situ regeneration for large scale applications. Finally, it discussed recovery of resources i.e., N₂O, NH₃ and N₂, the key challenges about several competitive side products and loss of catalytic activity over time to treat toxic gases via feasible solutions by hybrid wet scrubbing techniques.

Comparative Photo-Electrochemical and Photocatalytic Studies with Nanosized TiO2 Photocatalysts towards Organic Pollutants Oxidation

The size of TiO2 can significantly affect both its photocatalytic and photo-electrochemical properties, thus altering the photooxidation of organic pollutants in air or water. In this work, we give an account of the photo-electrochemical and photocatalytic features of some nanosized TiO2 commercial powders towards a model reaction, the photooxidation of acetone. Cyclic voltammograms (CV) of TiO2 particulate electrodes under UV illumination experiments were carried out in either saturated O2 or N2 solutions for a direct correlation with the photocatalytic process. In addition, the effect of different reaction conditions on the photocatalytic efficiency under UV light in both aqueous and gaseous phases was also investigated. CV curves with the addition of acetone under UV light showed a negative shift of the photocurrent onset, confirming the efficient transfer of photoproduced reactive oxygen species (ROSs), e.g., hydroxyl radicals or holes to acetone molecules. The photocatalytic experiments showed that the two nano-sized samples exhibit the best photocatalytic performance. The different photoactivity of the larger-sized samples is probably attributed to their morphological differences, affecting both the amount and distribution of free ROSs involved in the photooxidation reaction. Finally, a direct correlation between the photocatalytic measurements in gas phase and the photo-electrochemical measurements in aqueous phase is given, thus evincing the important role of the substrate-surface interaction with similar acetone concentrations.

Utilization of electrochemical treatment and surface reconstruction to achieve long lasting catalyst for NOx removal

The development of catalysts has seen tremendous growth recently but most strategies only report utilization of catalysts for a few initial cycles without taking into account the influence of oxygen poisoning. Here, the magnetic Fe₃O₄@EDTA-Fe (MEFe, having a core Fe₃O₄ particle with EDTA-Fe coating) was investigated as a model catalyst for long-term recycling for the removal of nitrogen oxide (NO_x) from NO/O₂ mixture, followed by N₂O recovery. The concentration of oxygen in the flue gas was found to have a strong impact on NO_x absorption and catalytic response. To circumvent the oxygen poisoning, the MEFe was subjected to electrochemical treatment in the presence of neutral red (N.R.) and NO removal efficiency was ∼95 % noted. Furthermore, the surface of the catalyst degraded significantly (p < 0.05) after 6-7 repetitive cycling due to surface catalytic reactions, surface poisoning, oxidation of metallic species as well as residual stresses. The MEFe surface was reconstructed after 7 cycles using EDTA solution and Fe source to achieve similar surface coating as the fresh MEFe catalyst. The reconstructed MEFe exhibited similar NO_x absorption capability as the fresh MEFe and the reconstruction loop was repeated several times to achieve long term cycling, which make the catalyst cost-effective. Hence, it is proposed that a successful regeneration process can be employed for promising, sustainable and long-lasting catalytic treatment of air pollutants.

Ultrafast conversion of carcinogenic 4-nitrophenol into 4-aminophenol in the dark catalyzed by surface interaction on BiPO4/g-C3N4 nanostructures in the presence of NaBH4

The heterogeneous catalytic conversion of pollutants into useful industrial compounds is a two-goals at once process, which is highly recommended from the environmental, economic, and industrial points of view.

Recent progress on the enhancement of photocatalytic properties of BiPO4 using π-conjugated materials

Semiconductor photocatalysis is regarded as most privileged solution for energy conversion and environmental application. Recently, photocatalysis methods using bismuth-based photocatalysts, such as BiPO₄, have been extensively investigated owing to their superior efficacy regarding organic pollutant degradation and their further mineralization into CO₂ and H₂O. It is well known that BiPO₄ monoclinic phase exhibited better photocatalytic performance compared to Degussa (Evonik) P25 TiO₂ in term of ultraviolet light driven organic pollutants degradation. However, its wide band gap, poor adsorptive performance and large size make BiPO₄ less active under visible light irradiation. However, extensive research works have been conducted in the past with the aim of improving visible light driven BiPO₄ activity by constructing a series of heterostructures, mainly coupled with π-conjugated architecture (e.g., conductive polymer, dye sensitization and carbonaceous materials). However, a critical review of modified BiPO₄ systems using π-conjugated materials has not been published to date. Therefore, this current review article was designed with the aim of presenting a brief current state-of-the-art towards synthesis methods of BiPO₄ in the first section, with an especial focuses onto its crystal-microstructure, optical and photocatalytic properties. Moreover, the most relevant strategies that have been employed to improve its photocatalytic activities are then addressed as the main part of this review. Finally, the last section presents ongoing challenges and perspectives for modified BiPO₄ systems using π-conjugated materials.

Recent Progress in Biochar-Based Photocatalysts for Wastewater Treatment: Synthesis, Mechanisms, and Applications

Biochar (BC) is a carbon-rich material produced from pyrolysis of biomass. In addition to its low toxicity, environmental compatibility, and low cost, BC has the desired advantages of well-developed mesoporous structure and abundant surface functional groups. In recent years, BC-based photocatalysts (BCPs) have played a significant role in many environmental fields. In this paper, we highlight the current progress and several exciting results of BCPs by focusing on their synthesis, characterization, mechanisms, and applications in wastewater treatment. Details on various preparation methods include sol–gel, hydrothermal/solvothermal, ultrasound, calcination, and in situ methods are summarized and discussed. The underlying mechanisms and the applications of BCPs for different semiconductors are reviewed. Furthermore, some future trends and potentials are outlined.

Digitally Printed AgNPs Doped TiO2 on Commercial Porcelain-Grès Tiles: Synergistic Effects and Continuous Photocatalytic Antibacterial Activity

In the present study, we use commercial digitally printed ceramic tiles, functionnalized by AgNPs doped micro–TiO2, to investigate the mechanism of Ag in the continouos photocatalytic antibacterial activity. The novelty of the research lies in the attempt to understand the mechanism of Ag, supported on TiO2, able to exhibit the same antibacterial activity of a standard system containing Ag species, but here, totally embedded on the tile surface, and thus not free to move and damage the bacteria cell. UV/vis diffuse reflectance spectroscopy (DRS) of AgNPs–TiO2 tiles indicated an enhanced visible light response, wherein a new absorption band was produced around 18,000–20,000 cm−1 (i.e., in the 400–600 nm range) owing to the surface plasmon resonance (SPR) of AgNPs. The antibacterial photocatalytic experiments were conducted towards the inactivation of E. coli under solar light and indoor light. It was found that the degradation speed of E. coli in the presence of AgNPs–TiO2 tiles is solar light-intensity depending. This justifies the semiconductor behavior of the material. Furthermore, the AgNPs–TiO2 tiles exhibit a high ability for the inactivation of E. coli at a high load (104–107 colony-forming unit (CFU)/mL). Additionally, AgNPs–TiO2 tiles showed a remarkable antibacterial activity under indoor light, which confirms the good photocatalytic ability of such tiles. On the basis of the reactive oxygen species (ROS) quenching experiments, O2•− species and h+ were more reactive for the inactivation of E. coli rather than •OH species. This is because of the different lifetime (bacteria are more likely oxidized by ROS with longer lifetime); in fact, O2•− and h+ exhibit a longer lifetime compared with •OH species. The generation of H2O2 as the most stable ROS molecule was also suggested.

One-pot fabrication of BiPO4/Bi2S3 hybrid structures for visible-light driven reduction of hazardous Cr(VI)

For the first time, a novel BiPO₄/Bi₂S₃ heterostructures with different morphologies have been fabricated through a facile and rapid one pot precipitation route followed by anion-exchange strategy for the photoreduction of toxic Cr(VI) to harmless Cr (III). The hybrid structures systematically investigated using XRD, FE-SEM, EDS, TEM, HRTEM, XPS, FT-IR, UV-vis DRS, and PL. Changing the solvent type has a significant role for controllable morphologies of BiPO₄/Bi₂S₃ hybrid as well as the catalytic activity. The BiPO₄/Bi₂S₃ hybrid synthesized in diethylene glycol (DEG) performed the highest reduction efficiency of Cr(VI) within 20 min, compared with pure hexagonal phase of BiPO₄ under visible light. The rate constant for BiPO₄/Bi₂S₃ synthesized in DEG found to be 20.3 times larger than that for pure BiPO₄. In addition, the presence of tartaric acid as hole scavenger could enhance the Cr(VI) reduction efficiency to 97.9%. No significant decrease in the catalytic efficiency after recycling up to four cycles. This promising study could present a significant approach towards Cr(VI) photoreduction from water through the novel BiPO₄/Bi₂S₃ photocatalyst.