Degradation of methylene blue by natural manganese oxides: kinetics and transformation products

Efficient dye removal using manganese oxide-modified nanocellulosic films from sugarcane bagasse

Removing toxic dyes from industrial wastewater is crucial for environmental protection. This research introduced novel composite films of manganese oxide (MnO2)-modified nanocellulose (MCel) and unmodified nanocellulose (Cel) derived from sugarcane bagasse for dye removal. Nanocellulose was extracted from sugarcane bagasse and subsequently transformed into MCel through in-situ MnO2 synthesis. The MCel/Cel composites, with various MCel to Cel ratios, were fabricated into films and evaluated for their efficiency in removing methylene blue (MB). The films were characterized using Fourier transform infrared spectroscopy for functional group analysis, X-ray diffraction for crystallinity, X-ray photoelectron spectroscopy for chemical state analysis, field emission scanning electron microscopy-energy dispersive spectroscopy for morphology and elemental composition, and Thermogravimetric Analysis for thermal behaviors. Adsorption results showed that all MCel/Cel composite films achieved over 97 % removal of MB (initial concentration 100 mg L-1) within 24 h, with convenient adsorbent retrieval after adsorption. The adsorption process followed a pseudo-second order kinetic model and Langmuir adsorption isotherm. The optimal 95:5 MCel/Cel film exhibited a rate constant of 6.16 × 10-4 g mg-1 min-1 and the calculated adsorption capacity of 181.85 mg g-1. These results demonstrate significant potential for wastewater treatment and sustainable waste valorization by converting sugarcane bagasse cellulose into environmentally friendly adsorbents for contaminant removal.

Synthesis and characterization of a novel copper carboxylate complex and a copper complex-coated polyether sulfone membrane for efficient degradation of methylene blue dye under UV irradiation: the single crystal X-ray structure of the copper carboxylate complex

Synthesis of a novel binuclear Cu(II) carboxylate complex under ambient laboratory conditions is presented. The complex exhibits a paddle wheel structure in which the axial positions are occupied by two copper atoms instead of two water molecules. The synthesized complex was characterized by single-crystal X-ray crystallography, FT-IR, X-ray diffraction, and UV-visible spectroscopy techniques. The thermal stability of the metal complex was studied by the thermogravimetric analysis study. The synthesized metal complex was employed for the synthesis of metal complex-coated polyether sulfone (PES) membranes which were characterized before and after filtration using the FESEM technique. The photocatalytic efficiency of the metal complex was studied for the degradation of methylene blue dye under UV irradiation in the presence of H2O2 and was compared with the photodegradation efficiency of the metal complex-coated polyether sulfone (PES) membrane.

Boron Nitride Nanosheet-Magnetic Nanoparticle Composites for Water Remediation Applications

The combination of 0D nanoparticles with 2D nanomaterials has attracted a lot of attention over the last years due to the unique multimodal properties of resulting 0D-2D nanocomposites. In this work, we developed boron nitride nanosheets (BNNS) functionalized with manganese ferrite magnetic nanoparticles (MNPs). The functionalization process involved attachment of MNPs to exfoliated BNNS by refluxing the precursor materials in a polyol medium. Characterization of the produced BNNS-MNP composites was carried out using powder X-ray diffraction, transmission electron microscopy, vibrating sample magnetometry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The adhesion of MnFe2O4 magnetic nanoparticles onto the BNNS remained unaffected by repeated sonication and heating in a furnace at 400 °C, underscoring the robust nature of the formed bond. FTIR spectra and XPS deconvolution confirmed the presence of strong bonding between BNNS and the MNPs. Membranes were fabricated from the BNNS and the BNNS-MnFe2O4 nanocomposites for evaluating their efficiency in removing the methylene blue dye pollutant. The membranes have been characterized by scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, and mercury intrusion porosimetry. The effectiveness of dye removal was monitored using ultraviolet-visible spectroscopy. The BNNS-MnFe2O4 nanocomposite membranes exhibited enhanced MB capture compared to membranes made from pure BNNS alone. The recyclability assessment of BNNS-MnFe2O4 demonstrated exceptional performance, retaining 92% efficiency even after eight cycles. These results clearly demonstrate the high potential of these magnetic nanocomposites as reusable materials for water filtration membranes. Furthermore, the introduction of magnetic functionality as part of the membrane brings an exciting opportunity for in situ magnetic heating of the membrane, which shall be explored in future work.

Electrophoretically deposited sulfonated poly(styrene-co-divinylbenzene) on a screw for microextraction of cationic dyes from aqueous solutions

In the present work, a novel solid-phase microextraction on a screw (MES) was employed to extract cationic dyes (malachite green, methylene blue, and rhodamine B) from food samples and fish breeding pool water. The sulfonated poly(styrene-co-divinylbenzene) was electrophoretically deposited on the surface of the grooves of a screw. Then the screw was placed inside a silicon tube as a holder to create a channel to run a test solution through it. The extracted dyes on the coated screw were eluted by a suitable eluent. High-performance liquid chromatography with an ultraviolet/visible detector was utilized for the separation and analysis of the analytes. The effective parameters of the analyte extraction efficiency were optimized. Under optimum conditions, the limits of detection were 0.15 μg/L, and calibration curves were linear in the range of 0.50-250.00 μg/L, with coefficients of determination > 0.989 for all studied dyes. The relative standard deviations of intra and inter-day (n = 3) were in the range of 2.8%-7.0% and 7.0%-9.5%, respectively. The MES was applied as a simple and repeatable method with acceptable relative recoveries (82.0%-103.0%) for the determination of cationic dyes in grape nectar, ice pop, jelly powder, and fish breeding pool water.

Toxic Effects of Methylene Blue on the Growth, Reproduction and Physiology of Daphnia magna

Methylene blue (MB) is a disinfectant used in aquaculture to prevent and treat fish diseases. However, the release of MB can pose a risk to the receiving water bodies. Zooplankton are the most sensitive organisms among aquatic life. Hence, this study examined the acute and chronic toxic effects of MB on zooplankton using Daphnia magna (D. magna) as a test organism to provide basic data for risk assessment. The results show that 48 h-EC₅₀ and 24 h-LC₅₀ were 61.5 ± 2.3 and 149.0 ± 2.2 μg/L, respectively. Chronic exposure to MB affected the heart rate, beat frequency of the thoracic limbs, and reproductive ability of D. magna at environmental concentrations higher than 4.7 μg/L. The cumulative molts, time to production of the first brood, and total number of living offspring were affected at different MB concentrations, while "abortions" were observed in high-exposure groups. The activity of superoxide dismutase was increased, while glutathione S-transferase activity was stimulated at low concentrations and inhibited at high concentrations. In addition, the malondialdehyde content increased with increasing concentrations of MB. Our findings demonstrate the impact of MB on the reproduction and growth of freshwater species, as well as their physiological responses. These results have implications for establishing guidelines on the use of MB in aquaculture and setting discharge standards.

Preparation of site-specific Z-scheme g-C3N4/PAN/PANI@LaFeO3 cable nanofiber membranes by coaxial electrospinning: Enhancing filtration and photocatalysis performance

The coaxial electrospinning method for preparation of g-C₃N₄/polyacrylonitrile (PAN)/polyaniline (PANI)@LaFeO₃ cable fiber membrane (PC@PL) was designed for adsorption-filtration-photodegradation of pollutants. A series of characterization results show that LaFeO₃ and g-C₃N₄ nanoparticles (NPs) are respectively loaded in the inner and outer layers of PAN/PANI composite fibers to construct the site-specific Z-type heterojunction system with spatially separated morphologies. The PANI in cable not only possesses abundant exposed amino/imino functional groups for adsorption of contaminant molecules but also due to the excellent electrical conductivity works as a redox medium for collecting and consuming the electrons and holes from LaFeO₃ and g-C₃N₄, which can efficiently promote photo-generated charge carriers separation and improve the catalytic performance. Further investigations demonstrate that as a photo-Fenton catalyst LaFeO₃ in PC@PL catalyzes/activates the H₂O₂ generated in situ by LaFeO₃/g-C₃N₄, further enhancing the decontamination efficiency of the PC@PL. The porous, hydrophilic, antifouling, flexible and reusable properties of the PC@PL membrane significantly enhance the mass transfer efficiency of reactants by filtration effect and increase the amount of dissolved oxygen, thus producing massive •OH for degradation of pollutants, which maintains the water flux (1184 L m^-2. h^-1 (LMH)) and the rejection rate (98.5%). Profiting from its unique synergistic effect of adsorption, photo-Fenton and filtration, PC@PL exhibits wonderful self-cleaning performance and distinguished removal rate for methylene blue (97.0%), methyl violet (94.3%), ciprofloxacin (87.6%) and acetamiprid (88.9%) within 75 min, disinfection (100% Escherichia coli (E. coli) and 80% Staphylococcus aureus (S.aureus) inactivation)) and excellent cycle stability.

Activation of peroxymonosulfate by base for degradation of methylene blue: role of bromide ions

Bromide ions are inevitable in aquatic environment and influence the degradation of contaminants in non-radical based advanced oxidation processes, but the role of reactive bromine species (RBS) remain obscure. This study investigated the role of bromide ions in the degradation of methylene blue (MB) during the base/peroxymonosulfate (PMS) process. The formation of RBS as a function of bromide ions were evaluated using a kinetic modelling. Bromide ions were shown to play crucial roles in MB degradation. Increasing the dosage of NaOH and Br^- increased the transformation kinetics of MB. However, brominated intermediates which are more toxic than precursor MB were generated in the presence of Br^-. The formation of adsorbable organic halides (AOX) was enhanced by elevating the dosage of Br^-. The formation of AOX was even more significant in the absence of NaOH, and the AOX values decreased with the increasing alkalinity. The kinetic model indicated that the dominant reactive species formed in the base/PMS/Br^- process are ¹O₂ and HOBr, and Br₂ in the Br^-/PMS process. Therefore, the influence of bromide ions should be taken into consideration in the application of the base/PMS process for organic matters in bromide-containing natural water. Strategies should be developed to make full use of RBS for the abatement of organic pollutants and to reduce the formation of AOX. This study reveals that in the treatment of saline wastewater by PMS-based processes, increasing the amount of NaOH may be an effective strategy to inhibit the accumulation of AOX.

Synthesis and Characterization of Orange Peel Modified Hydrogels as Efficient Adsorbents for Methylene Blue (MB)

In recent years, due to the developments in the textile industry, water contaminated with synthetic dyes such as methylene blue (MB) has become an environmental threat based on the possible impacts in terms of chemical and biochemical demand, which leads to disturbance in aquatic plants photosynthesis, besides their possible toxicity and carcinogenicity for humans. In this work, an adsorbent hydrogel is prepared via free radical polymerization comprising acrylic acid (PAA) as a monomer and orange peel (OP) as a natural modifier rich in OH and COOH present in its cellulose and pectin content. The resulting hydrogels were optimized in terms of the content of OP and the number of cross-linkers and characterized morphologically using Scanning electron microscopy. Furthermore, BET analysis was used to follow the variation in the porosity and in terms of the surface area of the modified hydrogel. The adsorption behavior was found to follow pseudo-second-order as a kinetic model, and Langmuir, Freundlich, and Temkin isotherm models. The combination of OP and PAA has sharply enhanced the adsorption percent of the hydrogel to reach 84% at the first 10 min of incubation with an adsorption capacity of more than 1.93 gm/gm. Due to its low value of pHPZc, the desorption of MB was efficiently performed at pH 2 using HCl, and the desorbed OP-PAA were found to be reusable up to ten times without a decrease in their efficiency. Accordingly, OP-PAA hydrogel represents a promising efficient, cost-effective, and environmentally friendly adsorbent for MB as a model cationic dye that can be applied for the treatment of contaminated waters.

Hectorite-CTAB-alginate composite beads for water treatment: kinetic, isothermal and thermodynamic studies

Encapsulation of hectorite-modified CTAB with Ca-alginate formed reusable adsorbent beads for wastewater treatment. The thermogravimetric analysis (TGA) investigation indicated excellent thermal stability results for BHec-40 compared to Hec-40. Although the mesoporous surface area of BHec-40 decreased to 79.74 m2 g-1 compared to 224.21 m2 g-1 for Hec-40, the hectorite-CTAB-alginate beads showed high adsorption capacity and stability for methyl orange (MO) adsorption with more than 60% removal after five adsorption-desorption cycles. The influence of pH (3-11), temperature (30, 40, and 50 °C), initial concentration (50-400 mg L-1), and contact time were studied to obtain the kinetics and thermodynamics of adsorption. The outcomes revealed a maximum monolayer adsorption capacity of 117.71 mg g-1 for BHec-40. The kinetics of adsorption demonstrated the suitability of using the pseudo-first-order kinetic model, while the equilibrium adsorption data follows the Langmuir isotherm. Thermodynamic analysis indicates physisorption of MO onto BHec-40. BHec-40 improves the reusability as an adsorbent for the removal of anionic dyes from aqueous media.

MnFe2O4@SiO2@CeO2 core–shell nanostructures for applications in water remediation†

Removal of dye pollutants from wastewater is among the most important emerging needs in environmental science and engineering. The main objective of our work is to develop new magnetic core–shell nanostructures and explore their use for potential removal of pollutants from water using an external magnetic field. Herein, we have prepared magnetic core–shell nanoparticles that demonstrated excellent dye pollutant adsorbent properties. These nanoparticles are composed of a manganese ferrite magnetic core coated with silica, to protect the core and enable further functionalisation, then finally coated with ceria, which is shown to be an effective adsorbent. The magnetic core–shell nanostructures have been synthesized by a modification of solvothermal synthesis. The nanoparticles were fully characterised at each stage of the synthesis by powder X-ray diffraction (pXRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM) and Fourier transform infrared spectroscopy (FTIR). These particles were found to be effective in removing methylene blue (MB) dye from water, which was validated by UV-visible (UV-vis) spectroscopy. These particles can be quickly removed from solution using a permanent magnet and then can be recycled after being placed in the furnace at 400 °C to burn off any organic residues. The particles were found to retain their ability to adsorb the pollutant after several cycles and TEM images of the particles after several cycles showed no change in the morphology. This research demonstrated the capacity of magnetic core–shell nanostructures to be used for water remediation.

Magnetic core–shell nanoparticles have been synthesised, characterised and used for methylene blue dye removal from water. They can be magnetically extracted and show no reduction in efficiency after several cycles.

Recent advances in biopolymer-based advanced oxidation processes for dye removal applications: A review

Over the past few years, synthetic dye-contaminated wastewater has attracted considerable global attention due to the low biodegradability and the ability of organic dyes to persist and remain toxic, causing numerous health and environmental concerns. As a result of the recalcitrant nature of those complex organic dyes, the remediation of wastewater using conventional wastewater treatment techniques is becoming increasingly challenging. In recent years, advanced oxidation processes (AOPs) have emerged as a potential alternative to treat organic dyestuffs discharged from industries. The most widely employed AOPs include photocatalysis, ozonation, Fenton oxidation, electrochemical oxidation, catalytic heterogeneous oxidation, and ultrasound irradiation. These processes involve the generation of highly reactive radicals to oxidize organic dyes into innocuous minerals. However, many conventional AOPs suffer from several setbacks, including the high cost, high consumption of reagents and substrates, self-agglomeration of catalysts, limited reusability, and the requirement of light, ultrasound, or electricity. Therefore, there has been significant interest in improving the performance of conventional AOPs using biopolymers and heterogeneous catalysts such as metal oxide nanoparticles (MONPs). Biopolymers have been widely considered in developing green, sustainable, eco-friendly, and low-cost AOP-based dye removal technologies. They inherit intriguing properties like biodegradability, renewability, nontoxicity, relative abundance, and sorption. In addition, the immobilization of catalysts on biopolymer supports has been proven to possess excellent catalytic activity and turnover numbers. The current review provides comprehensive coverage of different AOPs and how efficiently biopolymers, including cellulose, chitin, chitosan, alginate, gelatin, guar gum, keratin, silk fibroin, zein, albumin, lignin, and starch, have been integrated with heterogeneous AOPs in dye removal applications. This review also discusses the general degradation mechanisms of AOPs, applications of biopolymers in AOPs and the roles of biopolymers in AOPs-based dye removal processes. Furthermore, key challenges and future perspectives of biopolymer-based AOPs have also been highlighted.

Highly Efficient Industrial Dye Degradation, Bactericidal Properties, and In Silico Molecular Docking Analysis of Ag/Cellulose-Doped CuO Nanostructures

In this research, CuO nanostructures doped with Ag and cellulose nanocrystals (CNC) were synthesized using a facile coprecipitation technique. In this work, we doped Ag into fixed quantities of CNC and CuO to improve the photocatalytic, catalytic, and antibacterial activity. It was noted that catalytic activity increased upon doping, which was attributed to the formation of nanorods and a pH effect, while the reverse trend was observed in photocatalytic activity. The addition of Ag and CNC dopants into CuO improved the bactericidal efficacy for S. aureus and E. coli. In addition, to obtain insight into the possible mechanism behind their biocidal effects, molecular docking studies were conducted against specific enzyme targets: namely, dihydrofolate reductase from E. coli and DNA gyrase from S. aureus. This study suggested that codoped CuO could be highly efficient in the cleaning of polluted water and antibacterial applications.

Phyto Synthesis of Manganese-Doped Zinc Nanoparticles Using Carica papaya Leaves: Structural Properties and Its Evaluation for Catalytic, Antibacterial and Antioxidant Activities

The current study aims to synthesize bimetal oxide nanoparticles (zinc and manganese ions) using the carica papaya leaf extract. The crystallite size of the nanoparticle from X-ray diffraction method was found to be 19.23 nm. The nanosheet morphology was established from Scanning Electron Microscopy. Energy-dispersive X-ray diffraction was used to determine the elemental content of the synthesized material. The atomic percentage of Mn and Zn was found to be 15.13 and 26.63. The weight percentage of Mn and Zn was found to be 7.08 and 10.40. From dynamic light scattering analysis, the hydrodynamic diameter and zeta potential was found to be 135.1 nm and −33.36 eV. The 1,1-diphenyl-2-picryl hydroxyl radical, hydroxyl radical, FRAP, and hydrogen peroxide scavenging tests were used to investigate the antioxidant activity of Mn-Zn NPs. Mn-Zn NPs have substantial antioxidant properties. The photocatalytic activity of the Mn-Zn NPs was assessed by their ability to degrade Erichrome black T (87.67%), methyl red dye (78.54%), and methyl orange dye (69.79%). Additionally, it had significant antimicrobial action S. typhi showed a higher zone of inhibition 14.3 ± 0.64 mm. Mn-Zn nanoparticles were utilized as a catalyst for p-nitrophenol reduction. The bimetal oxide Mn-Zn NPs synthesized using C. papaya leaf extract exhibited promising dye degradation activity in wastewater treatment. Thus, the aforementioned approach will be a novel, low cost and ecofriendly approach.

Clay, Zeolite and Oxide Minerals: Natural Catalytic Materials for the Ozonation of Organic Pollutants

Ozone has been successfully employed in water treatment due to its ability to oxidize a wide variety of refractory compounds. In order to increase the process efficiency and optimize its economy, the implementation of heterogeneous catalysts has been encouraged. In this context, the use of cheap and widely available natural materials is a promising option that would promote the utilization of ozone in a cost-effective water treatment process. This review describes the use of natural clays, zeolites and oxides as supports or active catalysts in the ozonation process, with emphasis on the structural characteristics and modifications performed in the raw natural materials; the catalytic oxidation mechanism; effect of the operating parameters and degradation efficiency outcomes. According to the information compiled, more research in realistic scenarios is needed (i.e., real wastewater matrix or continuous operation in pilot scale) in order to transfer this technology to the treatment of real wastewater streams.

Studies of Clinoptilolite-Rich Zeolitic Tuffs from Different Regions and Their Activity in Photodegradation of Methylene Blue

The present study focuses on clinoptilolite (CLI)-rich natural zeolitic tuffs and their photocatalytic activity in the degradation of cationic organic dyes. CLI from different regions was tested in the photocatalytic degradation of methylene blue (MB) as a model cationic dye. The photocatalytic tests were performed at room temperature and atmospheric pressure under visible light irradiation. For all the CLI samples, the highest activity was observed at pH = 6. Total MB degradation varied between 70 and 91% (C0 = 10 mg dm–3, 0.2 g dm–3 of photocatalyst, during 300 min). It is suggested that the presence of Fe species in the studied tuffs is responsible for the photocatalytic activity. The activity increases linearly with the Fe content in the tuffs. The MB photodegradation follows the Langmuir–Hinshelwood kinetic model. The recyclability tests showed good stability and efficiency of the photocatalyst. The degradation rate decreased from 91 to 69% during three reaction cycles, indicating a promising potential of natural zeolites in the treatment of textile industry wastewater.

Review on Methylene Blue: Its Properties, Uses, Toxicity and Photodegradation

The unavailability of clean drinking water is one of the significant health issues in modern times. Industrial dyes are one of the dominant chemicals that make water unfit for drinking. Among these dyes, methylene blue (MB) is toxic, carcinogenic, and non-biodegradable and can cause a severe threat to human health and environmental safety. It is usually released in natural water sources, which becomes a health threat to human beings and living organisms. Hence, there is a need to develop an environmentally friendly, efficient technology for removing MB from wastewater. Photodegradation is an advanced oxidation process widely used for MB removal. It has the advantages of complete mineralization of dye into simple and nontoxic species with the potential to decrease the processing cost. This review provides a tutorial basis for the readers working in the dye degradation research area. We not only covered the basic principles of the process but also provided a wide range of previously published work on advanced photocatalytic systems (single-component and multi-component photocatalysts). Our study has focused on critical parameters that can affect the photodegradation rate of MB, such as photocatalyst type and loading, irradiation reaction time, pH of reaction media, initial concentration of dye, radical scavengers and oxidising agents. The photodegradation mechanism, reaction pathways, intermediate products, and final products of MB are also summarized. An overview of the future perspectives to utilize MB at an industrial scale is also provided. This paper identifies strategies for the development of effective MB photodegradation systems.

Controlled Synthesis and Structural Modulation to Boost Intrinsic Photocatalytic Activity of BiVO4

Modulation of the structure, composition, and morphology through a simple refinement of the synthetic parameters are central to obtaining signature catalytic properties, enabling an understanding of the underlying growth and...

Efficient Photocatalytic Degradation of Organic Dyes by AgNPs/TiO2/Ti3C2T x MXene Composites under UV and Solar Light

Due to their broad applications in various industrial activities, and their well-known negative impacts on the aquatic environment, organic dyes have been continuously identified as serious threat to the quality of ecosystems. The photocatalytic degradation process in aqueous solutions has emerged as an efficient and reliable approach for the removal of organic dyes. MXenes, a new class of two-dimensional (2D) nanomaterials, possess unique chemical composition, surface functionalities, and physicochemical properties. Such characteristics enable MXenes to act as efficient catalysts or cocatalysts to photodegrade organic molecules. This work explores the application of Ti₃C₂T _x MXene decorated with silver and palladium nanoparticles, using a simple hydrothermal treatment method, for the photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB). The chemical composition of these photocatalysts, as well as their structural properties and morphology, was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. The photocatalytic degradation abilities of the pristine MXene and the synthesized MXene composites were investigated under ultraviolet and solar light irradiation. A significant improvement in the photocatalytic performances was observed for all oxidized MXene composites when compared to pristine MXene, with a superior degradation efficiency achieved for AgNPs/TiO₂/Ti₃C₂T _x . This work broadens the application range of oxidized MXene composites, providing an alternative material for degrading organics dyes and wastewater treatment applications.

Preparation of C3N5 nanosheets with enhanced performance in photocatalytic methylene blue (MB) degradation and H2-evolution from water splitting

Ultrathin C₃N₅ nanosheets with enhanced photocatalytic methylene blue (MB) degradation and H₂-evolution performance were prepared from thermal treatment of 3-amino-1,2,4-triazole (3-AT) and NH₄Cl followed with a protonate procedure. The characterization results revealed that the protonating process could contribute to the exfoliation of C₃N₅ with large surface area, the effective charge transfer capability and the modified band structure. The as-prepared C₃N₅ nanosheets exhibited enhanced properties in photocatalytic reactions such as MB photodegradation and H₂-evolution from water splitting. This study offered a feasible route to prepare highly-efficient two-dimensional photocatalyst, which could be applied potentially for implementation in wide range of energy generation and environmental applications.

Time-resolved in situ monitoring of photocatalytic reactions by probe electrospray ionization mass spectrometry

Probe electrospray ionization mass spectrometry (PESI-MS) has been demonstrated to be a useful in situ and online analytical technique for monitoring of various reactions. In this work, PESI-MS with a surface-modified probe was adopted and applied to in situ monitoring of photocatalytic reactions. Typical reactions of semiconductor photocatalysts, namely TiO₂, SnO₂, WO₃, SiC and ZnS catalyzed methylene blue (MB) and brilliant green (BG) degradation, were selected to demonstrate the potential of PESI-MS to monitor heterogeneous photocatalytic reactions occurring in suspensions. Surface modification of the probe ensures increased wettability during the whole monitoring process. PESI-MS could provide continuous sampling and real-time MS results without time-consuming and cumbersome sample pretreatments. This method has other merits including good reproducibility and stability (time scale > 60 min), convenience of operation, low sample consumption, high time resolution and high tolerance to suspended photocatalyst particles. Time-resolved mass spectra and ion chromatograms of every chemical species e.g. the substrate and reactive intermediates could be obtained, which is helpful for a better understanding of the photocatalytic reaction process. Thus, PESI-MS could be a versatile analytical technique for in situ photocatalytic reaction analysis and could be an alternative means for the evaluation of photocatalyst performance.

New titania-based photocatalysts for hydrogen production from aqueous-alcoholic solutions of methylene blue

A series of CuO_x–TiO₂ photocatalysts were prepared using fresh and thermally activated Evonik Aeroxide P25 titanium dioxide. The photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, XANES, diffuse reflectance spectroscopy, and N₂ adsorption technique. Photocatalytic activity of the samples was tested in hydrogen production from aqueous-alcoholic solutions of methylene blue under UV radiation (λ = 386 nm). It was found for the first time the synergistic effect of hydrogen production from two substrates—dye and ethanol. The maximum hydrogen production rate in the system water–ethanol–methylene blue was 1 μmol min⁻¹, which is 25 times higher than a value measured in a 10% solution of ethanol in water. The thermal activation of titania also leads to a change in the rate of hydrogen production. The highest catalytic activity was observed for a CuO_x–TiO₂ photocatalyst based on titania thermally-activated at 600 °C in air. A mechanism of the photocatalytic reaction is discussed.

Simultaneous presence of ethanol and methylene blue was shown to provide the most efficient hydrogen production and methylene blue removal.