Semiconductor based photocatalysts for detoxification of emerging pharmaceutical pollutants from aquatic systems: A critical review

Visible-light-driven photocatalytic degradation of ibuprofen by Cu-doped tubular C3N4: Mechanisms, degradation pathway and DFT calculation

The copper-modified tubular carbon nitride (CTCN) with higher specific surface area and pore volume was prepared by a simple in-situ hydrolysis and self-assembly. Increased ∼4.7-fold and ∼2.3-fold degradation rate for a representative refractory water pollutant (Ibuprofen, IBP) were achieved with low-energy light source (LED, 420 ± 10 nm), as compared to graphitic carbon nitride (GCN) and tubular carbon nitride (TCN), respectively. The high efficiency of IBP removal was supported by narrow band gap (2.15 eV), high photocurrent intensity (1.10 μA/cm2) and the high surface -OH group (14.75 μg/cm3) of CTCN. According to analysis of the various reactive species in the degradation, the superoxide radical (•O2-) played a dominant role, followed by •OH and h+, responsible for IBP degradation. Furthermore, Fukui functions were employed to predict the active sites of IBP, and combined with the HPLC-MS/MS results, possible mechanisms and pathways for photocatalytic degradation were indicated. This study will lay an important scientific foundation and a possible new approach for the treatment of emerging aromatic organic pollutants in visible-light-driven heterogeneous catalytic oxidation environment.

Enhanced photo-Fenton-like performance of biotemplated manganese-doped cobalt silicate catalysts

Cobalt-based catalysts are one of the preferred materials for effective activation of hydrogen peroxide, and metal element doping and active site dispersion are effective methods to enhance their catalytic activity. In this work, manganese-doped cobalt silicate@diatomite composites with enhanced photo-Fenton-like oxidation performance were prepared and used for degradation of methyl orange (MO) dyes. Experiments showed that manganese doping increased the specific surface area of the samples and decreased the band gap energy of the materials. Moreover, the samples doped with manganese elements had better photo-Fenton-like properties. The degradation of methyl orange by Co0.25MnSi@DE/H2O2-UV reached more than 95%. In addition, density-functional theory (DFT) calculations showed that the Mn-doped samples were more prone to activate H2O2 than non-manganese-doped samples, and the synergistic effect from using a bimetallic catalyst increased the photo-Fenton oxidation activity in the system. ESR spectroscopy and bursting tests indicated that the possible degradation mechanism consisted of hydroxyl radicals and superoxide radicals generated by the synergistic effect of cobalt ions and manganese under UV radiation. This study thus presents a feasible idea for the preparation of cobalt-based photo-Fenton catalysts that also provides a basis for understanding the catalytic mechanism analysis of other types of bimetallic catalysts.

CaCu3Ti4O12 Perovskite Materials for Advanced Oxidation Processes for Water Treatment

The many pollutants detected in water represent a global environmental issue. Emerging and persistent organic pollutants are particularly difficult to remove using traditional treatment methods. Electro-oxidation and sulfate-radical-based advanced oxidation processes are innovative removal methods for these contaminants. These approaches rely on the generation of hydroxyl and sulfate radicals during electro-oxidation and sulfate activation, respectively. In addition, hybrid activation, in which these methods are combined, is interesting because of the synergistic effect of hydroxyl and sulfate radicals. Hybrid activation effectiveness in pollutant removal can be influenced by various factors, particularly the materials used for the anode. This review focuses on various organic pollutants. However, it focuses more on pharmaceutical pollutants, particularly paracetamol, as this is the most frequently detected emerging pollutant. It then discusses electro-oxidation, photocatalysis and sulfate radicals, highlighting their unique advantages and their performance for water treatment. It focuses on perovskite oxides as an anode material, with a particular interest in calcium copper titanate (CCTO), due to its unique properties. The review describes different CCTO synthesis techniques, modifications, and applications for water remediation.

One-step calcination synthesis of 2D/2D g-C3N4/WS2 van der Waals heterojunction for visible light-induced photocatalytic degradation of pharmaceutical pollutants

It is well-documented that accumulation of pharmaceutically active compounds (PhACs), such as antibiotics, in aquatic ecosystems is a prominent environmental hazard. Herein, a series of 2D materials-based heterojunctions, conceptualized based on the integration of graphitic carbon nitride (g-C₃N₄) with tungsten disulfide (WS₂), was fabricated through a facile one-step calcination process, and systematically evaluated for eliminating tetracycline (TC) and sulfamethoxazole (SMX) from aqueous matrices. The microstructure, optical properties, and surface chemistry of the as-prepared composites were examined with a range of microscopy and spectroscopy techniques. In comparison with pristine g-C₃N₄ or bare WS₂, the g-C₃N₄/WS₂ material, with optimal WS₂ loading, showed significantly improved photocatalytic activity, towards degradation of TC (84%) and SMX (96%), under visible light. Free radical scavenging experiments revealed that superoxide anions and hydroxyl radicals were predominantly responsible for the rapid breakdown of the PhACs. In addition, the dissociation intermediates and residues were identified and the plausible photocatalytic degradation pathways of TC and SMX over the as-constructed 2D/2D heterojunction were discussed. Further, the photocatalysis end products were non-toxic, as inferred via the resazurin cell viability assay, employing Escherichia coli as a model organism. Most importantly, the 2D/2D g-C₃N₄/WS₂ architecture was structurally resilient and exhibited a fairly stable cycling performance for persistent usage in wastewater treatment. The outcomes of this study testify that 2D/2D heterojunction of g-C₃N₄ fragments and WS₂ nanosheets holds great promise for destroying antibiotics or their metabolites, usually present in wastewaters.

Highly efficient visible light active doped metal oxide photocatalyst and SERS substrate for water treatment

The development of efficient nanomaterials with promising optical and surface properties for multifunctional applications has always been a subject of novel research. In this work, the study of highly efficient TiO₂ nanorods (NRs) and Ta-doped TiO₂ NRs (Ta-TiO₂ NRs) synthesized by alkaline hydrothermal treatment followed by soaking treatment has been reported. NRs were investigated for their potential applications as recyclable/reproducible visible light active photocatalysts and surface-enhanced Raman scattering (SERS) substrates in wastewater treatment. NRs were characterized by various microscopic (scanning and transmission electron microscopy), spectroscopic (X-ray diffraction, X-ray photoelectron, UV-visible, photoluminescence, and Raman spectroscopy), and surface (Brunauer-Emmett-Teller) techniques. The NRs exhibited promising optical properties with a band gap of 2.95 eV (TiO₂ NRs) and 2.58 eV (Ta-TiO₂ NRs) showing excellent photo-degradation activities for methylene blue (MB) dye molecules under natural sunlight. Particularly, Ta-TiO₂ NRs showed enhanced response as visible light active photocatalysts in normal sunlight and also as SERS substrate attributed to the additional defects introduced by Ta doping. It could be explained by the combined effect of doping-induced enhanced visible light absorption and charge transfer (CT) properties of Ta-TiO₂ NRs. Furthermore, Ta-TiO₂ NRs were investigated for their long-term stability, reproducibility of the data, and recyclability in view of their potential applications in water treatment.

Fenton Reaction–Unique but Still Mysterious

This study is devoted to the Fenton reaction, which, despite hundreds of reports in a number of scientific journals, provides opportunities for further investigation of its use as a method of advanced oxidation of organic macro- and micropollutants in its diverse variations and hybrid systems. It transpires that, for example, the choice of the concentrations and ratios of basic chemical substances, i.e., hydrogen peroxide and catalysts based on the Fe2+ ion or other transition metals in homogeneous and heterogeneous arrangements for reactions with various pollutants, is for now the result of the experimental determination of rather randomly selected quantities, requiring further optimizations. The research to date also shows the indispensability of the Fenton reaction related to environmental issues, as it represents the pillar of all advanced oxidation processes, regarding the idea of oxidative hydroxide radicals. This study tries to summarize not only the current knowledge of the Fenton process and identify its advantages, but also the problems that need to be solved. Based on these findings, we identified the necessary steps affecting its further development that need to be resolved and should be the focus of further research related to the Fenton process.

New Rare Earth-Doped Bilayered Perovskite Oxide Photocatalysts Sr2La0.5R0.5FeMnO7 (R = La, Nd, Sm, Gd, Dy) for the Degradation of Highly Toxic Methylene Blue Dye in Wastewater under Visible Light: Structural, Optical, and Magnetic Properties

This paper presents the rare earth doping effect on the structural, optical, and magnetic properties of bilayered Ruddlesden-Popper oxides Sr₂La_0.5R_0.5FeMnO₇ (R = La, Nd, Sm, Gd, Dy). Moreover, we are reporting for the first time a new rare earth-doped bilayered perovskite oxide series for the highly toxic methylene blue dye degradation in wastewater under visible light. Structural analysis of the PXRD data using the Rietveld refinements confirms the formation of the phases in tetragonal symmetry with the I4/mmm space group. The unit cell lattice parameters (a & c) and the cell volume (V) decrease monotonically from La- to Dy-doped samples owing to the decrease in the lanthanide ionic radii. The X-ray photoelectron spectroscopy analysis indicates the existence of the Mn ions in the mixed valence state. The DRS study shows that the energy band gap value decreases on moving from La to Gd substitution; however, it further increases for the Dy-doped sample. The magnetic measurements reveal that all the phases exhibit dominant anti-ferromagnetic interactions with Neel temperature (T _N) observed at 150, 147, 138, 113, and 117 K for La-, Nd-, Sm-, Gd-, and Dy-substituted phases, respectively. However, the presence of an unsaturated hysteresis loop observed in the isothermal magnetic field (H) vs magnetization (M) plot also indicates the existence of weak ferromagnetic interactions. The investigation of the photocatalytic activity of the synthesized samples was done by carrying out photo-oxidative degradation of methylene blue (MB) dye pollutants. The results show that the photodegradation enhances by doping with heavier rare earth ions with the exception of the Dy-doped sample. The Gd-doped catalyst shows the maximum degradation efficiency of 99.03% in 50 min under visible light irradiation. The scavenging experiments confirmed that the^·OH was the main/dominant oxidizing agent involved in the degradation of the MB dye.

Hydrothermally derived Cr-doped SnO2 nanoflakes for enhanced photocatalytic and photoelectrochemical water oxidation performance under visible light irradiation

Photocatalytic dye degradation is a method of environmental degradation that is commonly used to eliminate various pollutants produced by pharmaceutical and textile industries. Herein, pure and chromium (Cr)-doped SnO₂ nanoflakes were synthesized using a simple facile hydrothermal method and photocatalytic properties were studied under visible light illumination. In addition, photoelectrochemical (PEC) water oxidation properties were also studied using the prepared samples. Doping of transition metal ions introduces structural defects, which narrow the band gap of host sample, resulting in high catalytic activity. The synthesized doped SnO₂ displayed a rutile tetragonal crystal phase with a nanoflakes-like surface morphology having no other contaminations. The optical band gap of Cr-doped SnO₂ nanoflakes was significantly reduced (2.48 eV) over the pure sample (3.32 eV), due to successful incorporation of Cr ions into the host lattice. Furthermore, the dye removal efficiency of these nanoflakes was investigated for methyl orange (MO) and tetracycline (TC) organic contaminations. The Cr-doped SnO₂ nanoflakes exhibited superior photodegradation with 87.8% and 90.6% dye removal efficiency, within 90 min of light illumination. PEC water oxidation analysis showed that the doped photoelectrode achieved enhanced photocurrent density and showed a higher photocurrent density (1.08 mA cm^-2) over that of the undoped electrode (0.60 mA cm^-2). Electrochemical impedance spectroscopy (EIS) showed that doped electrodes exhibited lesser charge resistance than the pure electrode. The synthesized Cr-doped SnO₂ nanoflakes are suitable for water oxidation and photodegradation of organic pollutants. Thus, we strongly believe that the obtained results in this report will continue to provide new opportunities for the improvement of effective visible light photocatalysts for industrial wastewater treatment and water splitting for H₂ generation.

Photocatalytic assessed adsorptive removal of tinidazole from aqueous environment using reduced magnetic graphene oxide-bismuth oxychloride and its silver composite

Antibiotics (tinidazole (TNZ)) in wastewater, exhibit adverse effects on humans and ecosystem. The current study was aimed to synthesize photocatalysts mrGO/BiOCl and mrGO/BiOCl/Ag. mrGO was coupled with BiOCl by hydrothermal method and Ag was deposited over it. The synthesized mrGO/BiOCl and mrGO/BiOCl/Ag were confirmed by Pzc analysis (5.5 and 4.4 for mrGO/BiOCl and mrGO/BiOCl/Ag, respectively), surface area analysis (380 m² g^-1, 227.7 m² g^-1, 220 m² g^-1 for mrGO, mrGO/BiOCl and mrGO/BiOCl/Ag respectively), elemental analysis (Ag, O, Bi, Fe), surface morphology (rough ball like sphere of mrGO/BiOCl and cubic Ag nanoparticles in mrGO/BiOCl/Ag), functional groups and band gap (Eg) determination. The Eg was determined using Kubelka-Munk equation as 3.5 and 2.8 eV for mrGO/BiOCl and mrGO/BiOCl/Ag respectively. During the adsorption study, the best experimental conditions for various operating parameters such as pH (2), contact time (5 min for mrGO/BiOCl and 10 min for mrGO/BiOCl/Ag under UV irradiation), TNZ concentration (18 μgL^-1) and catalyst dosage (0.001 g) were achieved. Kinetic study revealed that both composites followed pseudo second order kinetics (R² = 0.9979 and 0.9986, respectively). Data of rGO/BiOCl was fitted to Freundlich adsorption model (R² = 0.9687) and rGO/BiOCl/Ag fitted to Langmuir adsorption model (R² = 0.9994). Moreover, thermodynamic parameters confirmed that a photodegradation phenomenon was spontaneous and exothermic. The results confirmed that rGO/BiOCl and rGO/BiOCl/Ag are appropriate composites for TNZ removal from the aqueous environment with removal efficiency of 97 and 24%, respectively.

Nanoarchitecture of graphene nanosheets decorated with NiCr layered double hydroxide for sonophotocatalytic degradation of refractory antibiotics

Highly efficient and durable catalysts for wastewater treatment are urgently required to tackle critical environmental issues. In this regard, NiCr LDH (NC), NiCr LDH-GO (NC-GO), and NiCr LDH-rGO (NC-rGO) nanocomposites were synthesized. The results of XRD, EDX, and FTIR analyses not only explored the crystallographic and chemical structures of catalysts but also confirmed the successful synthesis. Further morphological, physical, chemical, and optical characteristics of the catalysts were evaluated more by SEM, HRTEM, BET, DRS, and XPS techniques. The as-synthesized catalysts were used for the efficient mineralization of rifadin under 50 W LED visible light irradiation and the ultrasonic power of 150 W. Amongst, 0.75 g L^-1 of NC-rGO demonstrated high sonophotocatalytic efficiency (88%) in natural pH (pH = 8) of 15 mg L^-1 of rifadin. The introduced system is also powerful for the decontamination of pharmaceutical-containing wastewater as well as other refractory antibiotics. Moreover, the radical trapping experiments demonstrated that the main reactive species involved in the degradation of rifadin are ^•OH, h⁺, and O₂^•-. The possible intermediates were thoroughly investigated using GCMS analysis. Also, NC-rGO demonstrated superior antibacterial activity in comparison with NC, NC-GO samples.

Lignosulfonate valorization into a Cu-containing magnetically recyclable photocatalyst for treating wastewater pollutants in aqueous media

This study presents an eco-friendly and economical process for preparing a magnetic copper complex conjugated to modified calcium lignosulfonate (LS) through a diamine (Fe₃O₄@LS@naphthalene-1,5-diamine@copper complex; FLN-Cu) as a green and novel catalyst. The prepared catalyst was characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), Brunauer-Emmett-Teller (BET), energy-dispersive X-ray spectroscopy (EDS), elemental mapping, inductively coupled plasma-optical emission spectrometry (ICP-OES) and field emission scanning electron microscopy (FESEM) techniques. The photocatalytic performance of the synthesized FLN-Cu catalyst was investigated by the degradation of aqueous solutions of dyes such as Rhodamine B (RhB), methylene blue (MB), and Congo red (CR) under UV irradiation. The dye degradation was followed by UV-Vis (ultraviolet-visible) spectrophotometry by measuring the changes in absorbance. The effects of different factors such as pH, contact time, photocatalyst dosage, and initial concentration of dye on the adsorption percentage were also investigated. Moreover, the catalyst showed high stability and could be readily separated from the reaction media using a magnet and reused five times without a remarkable loss of catalytic ability.

Electrochemical Sensing of Favipiravir with an Innovative Water-Dispersible Molecularly Imprinted Polymer Based on the Bimetallic Metal-Organic Framework: Comparison of Morphological Effects

Molecularly imprinted polymers (MIPs) are widely used as modifiers in electrochemical sensors due to their high sensitivity and promise of inexpensive mass manufacturing. Here, we propose and demonstrate a novel MIP-sensor that can measure the electrochemical activity of favipiravir (FAV) as an antiviral drug, thereby enabling quantification of the concentration of FAV in biological and river water samples and in real-time. MOF nanoparticles’ application with various shapes to determine FAV at nanomolar concentrations was described. Two different MOF nanoparticle shapes (dodecahedron and sheets) were systematically compared to evaluate the electrochemical performance of FAV. After carefully examining two different morphologies of MIP-Co-Ni@MOF, the nanosheet form showed a higher performance and efficiency than the nanododecahedron. When MIP-Co/Ni@MOF-based and NIP-Co/Ni@MOF electrodes (nanosheets) were used instead, the minimum target concentrations detected were 7.5 × 10−11 (MIP-Co-Ni@MOF) and 8.17 × 10−9 M (NIP-Co-Ni@MOF), respectively. This is a significant improvement (>102), which is assigned to the large active surface area and high fraction of surface atoms, increasing the amount of greater analyte adsorption during binding. Therefore, water-dispersible MIP-Co-Ni@MOF nanosheets were successfully applied for trace-level determination of FAV in biological and water samples. Our findings seem to provide useful guidance in the molecularly imprinted polymer design of MOF-based materials to help establish quantitative rules in designing MOF-based sensors for point of care (POC) systems.

Simultaneous determination of hydrochlorothiazide, amlodipine, and telmisartan with spectrophotometric and HPLC green chemistry applications

For the quantifiable amounts of Telmisartan (TLM) and Hydrochlorothiazide (HYD) in the presence of Amlodipine (AML) in a ternary mixture of synthetic laboratory mixture, a novel, sensitive, quick, and practical reversed-phase high-performance liquid chromatography (RP-HPLC) method was given. In order to separate, a Waters Spherisorb ODS-2 C18 column was used. For HYD, TLM, and AML, these techniques were viable over linearity ranges of 4-12 μg/mL, 4-25 μg/mL, and 5-40 μg/mL, respectively. The mobile phase system was acetonitrile:methanol: phosphate buffer at pH 2.5 (65:5:30 v/v/v), and the flow rate was 1.5 mL/min. Novel spectrophotometric methods were applied for active substances to determine simultaneously. The first method is absorptivity centering using factorized spectrum, and the second method is dual amplitude difference coupled with absorbance subtraction. These approaches have been effectively applied to bulk, laboratory synthetic mixtures to employ active components quantitatively. Correlation coefficients were found to be higher than 0.99 and the limit of detection values lower than 0.49 μg/mL in both spectrophotometric methods. The methodologies were validated following ICH recommendations. In the developed HPLC method, the limit of detection values was found to be 0.01 μg/mL for HYD and 0.02 μg/mL for AML and TLM. The correlation coefficients for the HPLC method were found to be 0.9971 for HYD, 0.9990 for AML, and 0.9983 for TLM. The suggested HPLC technique is a simple, effective, sensitive, environmentally friendly, and time-saving approach for determining TLM and HYD in the presence of AML.

Natural and anthropogenic origin of metallic contamination and health risk assessment: A hydro-geochemical study of Sehwan Sharif, Pakistan

Heavy metal contamination in groundwater is a serious threat to the environment and therefore its proper monitoring is a matter of great concern these days. In the present research, groundwater samples from Sehwan Sharif district Jamshoro, Pakistan were collected to estimate the concentration of various elements including potentially hazardous metals. Statistical analysis of the collected data based on Pearson co-relation metal clustering and Principal Component Analysis (PCA) divides the elements into three groups; Group I contains As, Cu, Ni, and Cd, Group II contains Mn, Fe, B, and Cr and Group III contains Pb and Zn. The elements Cu, Ni, As, Pb, Cd, and Zn found with higher RSD values demonstrate their anthropogenic origin whereas the lower concentration of Mn, Fe, B, and Cr indicate their natural origin (Tepanosyan et al., 2016). The histograms and box-plots of Mn, Fe, B and Cr were found normally distributed while abnormal for Cu, Ni, Pb, As, Cd and Zn. The HQs of these elements indicate their non-carcinogenic risks. However, results of individual metallic behavior indicate the highest HQ measured for B followed by HQs for Cu, and As. The toxic effects of investigated metal (loid)s calculated using HI were found to be 1.58 for adults and 1.35 for the child which is considered the medium chromic risk and cancer risk. About the toxicity of these heavy metals, their cancer risk was assessed on the levels of Cd, As, and Cr in groundwater. The carcinogenic risk of As was found to be 2.78 × 10^-4 and 1.62 × 10^-3 for child and adult, respectively. Furthermore, the values of this carcinogenic risk are 2.64 × 10^-6 and 1.54 × 10^-5 for Cd while 4.24 × 10^-3 and 2.48 × 10^-2 for Cr in child and adult, respectively. Since cancer risk exceeded the target risk of 1 × 10^-4 for As and Cr in adults and children, it can thus be considered 'non-acceptable'. The Geographic Information System (GIS) based maps were prepared using Inverse Distance Weighted (IDW) interpolation which showed the Spatial distribution of all elements throughout Sehwan Sharif from different sources of environment. Spatial maps of elements produced by ArcGIS show the hotspots of potentially hazardous elements such as the highest concentration of Pb, As, Zn, Cu, Ni, and Cd were found in urban areas of Sehwan Sharif district Jamshoro, Pakistan.

Synthesis of TiC@C-anatase/rutile@polyvinyl alcohol/xylan: a powerful photocatalyst for degradation of organic pollutant under visible light

In this study, a composite bearing titanium carbide (TiC), titanium dioxide (TiO₂), polyvinyl alcohol and xylan (TiC@C-anatase/rutile@polyvinyl alcohol/xylan) was synthesized and applied as a photocatalyst for the degradation of bromophenol blue (BPB) solution through several steps. Nanostructure of TiC and TiO₂ in the anatase and rutile phases was obtained through heat treatment of TiC at different times and temperatures (TiC@AR) which led to a reduction in energy bandgap from UV to visible light, in addition to the enhancement of the surface activity. After TiC@AR polymerization by xylan and polyvinyl alcohol and obtaining TiC@AR/PX, the energy bandgap reduced to IR range (52% of the sunlight) while showing an enhancement in the surface activity. The photocatalytic activity of the compounds was tested by studying the decomposition of BPB solution under visible light. The result illustrated the ability of TiC and TiC@AR to decrease the concentration of BPB after 150 min by 35% and 37%, respectively, while this reduction was 72% for TiC@AR/PX. Considering the effective parameters, the energy bandgap and the surface layer played key roles in photocatalytic degradation.

Photocatalytic Degradation of Some Typical Antibiotics: Recent Advances and Future Outlooks

The existence of antibiotics in the environment can trigger a number of issues by fostering the widespread development of antimicrobial resistance. Currently, the most popular techniques for removing antibiotic pollutants from water include physical adsorption, flocculation, and chemical oxidation, however, these processes usually leave a significant quantity of chemical reagents and polymer electrolytes in the water, which can lead to difficulty post-treating unmanageable deposits. Furthermore, though cost-effectiveness, efficiency, reaction conditions, and nontoxicity during the degradation of antibiotics are hurdles to overcome, a variety of photocatalysts can be used to degrade pollutant residuals, allowing for a number of potential solutions to these issues. Thus, the urgent need for effective and rapid processes for photocatalytic degradation leads to an increased interest in finding more sustainable catalysts for antibiotic degradation. In this review, we provide an overview of the removal of pharmaceutical antibiotics through photocatalysis, and detail recent progress using different nanostructure-based photocatalysts. We also review the possible sources of antibiotic pollutants released through the ecological chain and the consequences and damages caused by antibiotics in wastewater on the environment and human health. The fundamental dynamic processes of nanomaterials and the degradation mechanisms of antibiotics are then discussed, and recent studies regarding different photocatalytic materials for the degradation of some typical and commonly used antibiotics are comprehensively summarized. Finally, major challenges and future opportunities for the photocatalytic degradation of commonly used antibiotics are highlighted.

Green Synthesis of CS-TiO2 NPs for Efficient Photocatalytic Degradation of Methylene Blue Dye

The development of a non-malignant and sustainable treatment approach for eradicating mephitic organic dyes from freshwater resources is a daunting task. In a similar vein, the current work investigates the mitigation of methylene blue (MB) dye utilizing titanium dioxide nanoparticles (CS-TiO₂ NPs) synthesized using cannabis sativa (bhang) leaf extract via a greener approach. The CS-TiO₂ NPs are well characterized through XRD, FE-SEM, HR-TEM, UV-Vis spectroscopy, FTIR spectroscopy, and EDS spectroscopy. Microscopic studies confirm that the average particle size distribution of the individual particles was found to be in the range of 12.5 ± 1.5 nm, whereas the average size of the CS-TiO₂ NPs aggregates is 24.5 ± 11.5 nm. Additionally, the synthesized CS-TiO₂ NPs manifested remarkable photocatalytic degradation potential against methylene blue dye with a degradation efficiency of 98.2% and an apparent rate constant of 0.0398 min⁻¹. As a result, this research offers a green/sustainable alternative for water purification.

Degradation of toxic agrochemicals and pharmaceutical pollutants: Effective and alternative approaches toward photocatalysis

Emerging concern regarding the remediation of environmental pollution has expanded tremendously in recent years. Pharmaceutical industries and agricultural sectors release an enormous amount of residues containing toxic pollutants at trace levels which poses a serious impact on the environment and human health. To cope with the effect of hazardous and toxic contaminants, numerous methodologies have been developed for the treatment of effluents released from the agrochemical and pharmaceutical industries. Amongst them, photocatalysis has gained much more attention for the degradation of pollutants due to its low cost, higher capability, green and eco-friendly approaches. Photocatalysts are the substrate that plays a key role in pollutant removal through photocatalysis by accelerating the necessary chemical reactions using a light source. In this review, the recent progress on photocatalysis and its fundamental mechanism in agrochemicals and pharmaceutical pollutant degradation was summarized. This review concisely discusses the incorporation of various metal oxides and nanomaterials into semiconductors for the effective degradation of contaminants. The current status and future research on different sectors and the difficulties in the photocatalytic removal of agrochemical and pharmaceutical pollutants are also reviewed in detail.

Multifunctional Photocatalytic Filter Paper Based on Ultralong Nanowires of the Calcium-Alendronate Complex for High-Performance Water Purification

Semiconductor photocatalysts and membrane separation technology have been widely used in the field of water treatment. Usually, the particles of traditional semiconductor photocatalysts are easy to aggregate, difficult to separate from the liquid phase after photocatalysis, and may even cause secondary pollution. On the other hand, the membrane separation technology is also facing the problem of sharp decreases in removal efficiency and water flux caused by the membrane fouling. However, it is an attractive and promising solution to combine two technologies of photocatalysis and membrane separation for high-performance water treatment. In this work, we have developed the calcium oleate precursor solvothermal method to synthesize ultralong nanowires (UNWs) of Ca-alendronate (Ca-ALN) complex for the first time. Experimental results and data analysis indicate that the as-prepared Ca-ALN ultralong nanowires are an n-type semiconductor with an energy band gap of 3.41 eV. A new type of multifunctional photocatalytic filter paper has been developed based on ultralong nanowires of Ca-ALN complex (Ca-ALN-UNWs) and cellulose fibers (CFs). The as-prepared Ca-ALN-UNW/CF photocatalytic filter paper exhibits multifunctions of photocatalysis, adsorption, and filtration, which can be used for high-performance treatment of the wastewater containing various pollutants such as heavy-metal ions, dyes, antibiotics, and bacteria. The active oxygen species produced by the Ca-ALN-UNW/CF photocatalytic filter paper under light illumination are determined by electron spin resonance, and the energy band gap and photoelectric properties of the material are tested by ultraviolet-visible diffuse reflectance spectroscopy and electrochemical workstation. The pure water flux of the Ca-ALN-UNW/CF photocatalytic filter paper is very high, which can reach 2230.5 L m^-2 h^-1 under a working pressure of 0.1 MPa. The Ca-ALN-UNW/CF photocatalytic filter paper is promising for various applications such as highly efficient water purification and in the biomedical field.

Decontamination of emerging pharmaceutical pollutants using carbon-dots as robust materials

Environmental pollution is a critical issue that requires proper measures to maintain environmental health in a sustainable and effective manner. The growing persistence of several active pharmaceutical residues, such as antibiotics like tetracycline, and anti-inflammatory drugs like diclofenac in water matrices is considered an issue of global concern. Numerous sewage/drain waste lines from the domestic and pharmaceutical sector contain an array of toxic compounds, so-called "emerging pollutants" and possess adverse effects on entire living ecosystem and damage its biodiversity. Therefore, effective solution and preventive measures are urgently required to sustainably mitigate and/or remediate pharmaceutically active emerging pollutants from environmental matrices. In this context, herein, the entry pathways of the pharmaceutical waste into the environment are presented, through the entire lifecycle of a pharmaceutical product. There is no detailed review available on carbon-dots (CDs) as robust materials with multifunctional features that support sustainable mitigation of emerging pollutants from water matrices. Thus, CDs-based photocatalysts are emerging as an efficient alternative for decontamination by pharmaceutical pollutants. The addition of CDs on photocatalytic systems has an important role in their performance, mainly because of their up-conversion property, transfer photoinduced electron capacities, and efficient separation of electrons and holes. In this review, we analyze the strategies followed by different researchers to optimize the photodegradation of various pharmaceutical pollutants. In this manner, the effect of different parameters such as pH, the dosage of photocatalyst, amount of carbon dots, and initial pollutant concentration, among others are discussed. Finally, current challenges are presented from a pollution prevention perspective and from CDs-based photocatalytic remediation perspective, with the aim to suggest possible research directions.

Reduction of nitrates in a photocatalytic membrane reactor in the presence of organic acids

The present study explores the capability of the Photocatalytic Membrane Reactor (PMR) technology to remove nitrates from drinking water sources in the presence of organic electron donors. A systematic investigation was performed in a laboratory-pilot PMR, employing a hybrid TiO₂/UV-A catalysis-ultrafiltration process, using formic acid as the most favorable hole scavenger for nitrate reduction. The naturally occurring humic acid as well as the cheaper and harmless acetic acid were also tested as sacrificial electron donors. The performance of the PMR system was evaluated in respect of nitrate and Total Organic Carbon (TOC) percentage removal. The results demonstrate the superiority of formic acid regarding nitrate reduction, followed by acetic acid and humic acid, as well as the negligible effect of nitrates on organic mineralization. Formic acid was further used to assess the effects of molar organic/nitrate ratio, catalyst dosage and power of irradiation per unit volume (P_R) on nitrate reduction. With the present laboratory-pilot, the near optimum nitrate removal was ~60 % and the TOC reduction ~85 %; selectivity to dinitrogen was in the range 65-90 %. Key issues for improving this synergistic process and related R&D directions are discussed.

WO3/Ag2CO3 Mixed Photocatalyst with Enhanced Photocatalytic Activity for Organic Dye Degradation

The development of an efficient photocatalyst with superior activity under visible light has been regarded as a significant strategy for pollutant degradation and environmental remediation. Herein, a series of WO₃/Ag₂CO₃ mixed photocatalysts with different proportions were prepared by a simple mixing method and characterized by XRD, SEM, TEM, XPS, and DRS techniques. The photocatalytic performance of the WO₃/Ag₂CO₃ mixed photocatalyst was investigated by the degradation of rhodamine B (RhB) under visible light irradiation (λ > 400 nm). The photocatalytic efficiency of the mixed WO₃/Ag₂CO₃ photocatalyst was rapidly increased with the proportion of Ag₂CO₃ up to 5%. The degradation percentage of RhB by WO₃/Ag₂CO₃-5% reached 99.7% within 8 min. The pseudo-first-order reaction rate constant of WO₃/Ag₂CO₃-5% (0.9591 min^-1) was 118- and 14-fold higher than those of WO₃ (0.0081 min^-1) and Ag₂CO₃ (0.0663 min^-1). The catalytic activities of the mixed photocatalysts are not only higher than those of the WO₃ and Ag₂CO₃ but also higher than that of the WO₃/Ag₂CO₃ composite prepared by the precipitation method. The activity enhancement may be because of the easier separation of photogenerated electron-hole pairs. The photocatalytic mechanism was investigated by free radical capture performance and fluorescence measurement. It was found that light-induced holes (h⁺) was the major active species and superoxide radicals (·O₂ ^-) also played a certain role in photocatalytic degradation of RhB.

An activated carbon fiber supported Fe2O3@bismuth carbonate heterojunction for enhanced visible light degradation of emerging pharmaceutical pollutants

The developed Fe2O3@BC heterojunction photocatalyst supported over activated carbon fiber exhibited efficient photocatalytic activity for degradation of antipyrine under visible light irradiation.

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.