Natural sunlight driven highly efficient photocatalysis for simultaneous degradation of rhodamine B and methyl orange using I/C codoped TiO2 photocatalyst

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

Efficient removal of methyl orange and ciprofloxacin by reusable Eu-TiO2/PVDF membranes with adsorption and photocatalysis methods

The presence of methyl orange (MO) and ciprofloxacin (CIP) in wastewater poses a serious threat to the environment and human health. Titanium dioxide nanoparticles (TiO2 NPs) are widely studied as photocatalysts for wastewater treatment. However, TiO2 NPs have the drawbacks of high energy required for activation, fast electron-hole pair recombination and difficulty in recovering from water. To overcome these problems, europium decorated titanium dioxide/poly(vinylidene fluoride) (Eu-TiO2/PVDF) membranes were successful prepared in this work by combining the modified sol-gel method and the immersion phase inversion method. The Eu-TiO2/PVDF membranes obtained with the increase of Eu-TiO2 NPs content during the preparation process were named M1, M2 and M3, respectively. The pure PVDF membrane without the addition of Eu-TiO2 NPs was named M0, which was prepared by the immersion phase inversion method and served as a reference. The prepared Eu-TiO2/PVDF membranes could not only adsorb MO, but also degrade CIP under visible-light irradiation. Moreover, the Eu-TiO2/PVDF membranes exhibited adsorption-photocatalytic activity towards a mixture of MO and CIP under visible-light irradiation. Last but not the least, the Eu-TiO2/PVDF membranes exhibited excellent recyclability and reusability, opening the avenue for a possible use of these membranes in sewage-treatment plants.

Photodegradation of rhodamine-B in aqueous environment using visible-active gC3N4@CS-MoS2 nanocomposite

Rapid industrial expansion leads to environmental pollution especially in an aqueous environment. Photocatalytic degradation is one of the most efficient and environmentally friendly techniques used to treat industrial pollution due to its complete degradation capability of a variety of water contaminants to their non-toxic state. Graphitic carbon nitride (gC3N4) and molybdenum disulfide (MoS2) provide efficient dye degradation, but MoS2 has few disadvantages. Hence, chitosan (CS) supported gC3N4-MoS2 hybrid nanocomposite was developed in this study to reduce these issues by accelerating the degradation of dye molecules such as rhodamine-B under visible light. The prepared gC3N4@CS-MoS2 hybrid nanocomposite was thoroughly characterized using various analytical tools including FTIR, XRD, SEM, EDX, XPS, UV-Visible, and PL spectra. Several influencing parameters such as irradiation time, initial pH, dosage, and initial dye concentration were optimized by batch mode. The photodegradation of rhodamine-B could be induced by the heterogeneous gC3N4@CS-MoS2-water hybrid nanocomposite. The narrow band gap of gC3N4@CS-MoS2 (1.80 eV) makes it suitable for effective degradation of rhodamine-B due to more active in the visible region and attained its highest degradation efficiency of 99% after 40 min at pH 8 with minimum dosage of 60 mg. The possible degradation mechanism was tentatively proposed for rhodamine-B dye molecules from aqueous environment. The present work shows a novel photocatalyst for the purification and detoxification of dye molecules as well as other water contaminants found in polluted wastewater.

Synergistic effects of multitype carbon doping and oxygen vacancies in TiO2/CNTs composite fabricated via nonthermal plasma for formaldehyde removal

Formaldehyde as one of the typical indoor pollutants has long been concerned as it can pose a threat to human health. TiO2/CNTs composite with oxygen vacancies and multitype carbon doping (C-TiO2/CNTs) was fabricated using nonthermal plasma for the photocatalytic degradation of formaldehyde. The maximum degradation rate of formaldehyde was 93% and 83% via the new catalyst (with 5% CNTs content) under solar and visible light, respectively. The characterization of the catalyst confirmed the in-situ multitype carbon doping and oxygen vacancies: interstitial carbon doping and oxygen vacancies could dramatically reduce the bandgap and contribute to the improved absorption capability of formaldehyde and electrons. Interfacial carbon doping in the form of C-O-Ti bonds provided a migration channel, whereby photogenerated electrons could efficiently transfer from CNTs to TiO2 and then quench the holes left in the VB of TiO2. Therefore, the multitype carbon doping and oxygen vacancies can expand the light response as well as promote the separation of photo-generated electron/hole pairs. EPR results and experiment section indicated that O2·- plays the most significant role in formaldehyde removal due to the reverse transfer of the electrons. This work advances the understanding of photo-degradation of TiO2/CNTs composite and provides a new route for the abatement of formaldehyde.

Photocatalytic Aryl Sulfide Oxidation Using 4-Nitrophenylacetylene-Modified Cu2O Crystals

4-Nitrophenylacetylene-functionalized Cu₂O rhombic dodecahedra and cubes have been used to photocatalyze aryl sulfide oxidation generating aryl sulfoxides. With an oxygen supply and light from a blue light-emitting diode (LED), the reaction can be completed in 12 h with a water and methanol mixed solution. Generally high product yields and excellent product selectivity of sulfoxides over sulfones were achieved. In particular, a thioanisole to methyl phenyl sulfoxide yield of 98% was obtained. A mechanistic study has revealed that photogenerated electrons, holes, and superoxide radicals are involved in the oxidation reaction. The benefit of simple photocatalyst preparation and molecular functionalization to boost catalytic performance shows that surface-controlled ionic solids can be very effective photocatalysts for some organic transformations.

A sustainable and green chlorophyll/TiO2:W composite supported on recycled plastic bottle caps for the complete removal of Rhodamine B contaminant from drinking water

This investigation reports the photocatalytic performance of the tungsten doped titania (TiO₂:W or TW) with and without coating of chlorophyll (Chl) for the removal of the RhB dye from the drinking water. These particles were also supported on recycled plastic bottle caps (Bcap) to form other photocatalytic composites (TW/Bcap and TW + Chl/Bcap). The SEM images demonstrated that the TW particles without Chl had irregular shapes and sizes of 0.8-12 μm. The TW particles coated by the Chl presented shapes of quasi-rounded grains and smaller particle sizes of 0.8-1.8 μm. The photocatalytyic experiments showed that the photocatalyst powders containing Chl removed completely the RhB dye from the water after 2h under UV-VIS light, while the photocatalyst without Chl removed a maximum of 95% of the RhB. Interestingly, the TW/Bcap and TW + Chl/Bcap composites removed 94-100% of the RhB after 2h. Those ones removed such dye by photocatalysis and by physical adsorption at the same time (as confirmed by the absorbance and FTIR measurements), therefore, the removal of RhB was still very high. Scavenger experiments were also achieved and found that the •OH radicals are the main oxidizing species generated by the photocatalysts with and without Chl. The •O₂^- radicals and holes (h⁺) were the secondary oxidizing species. The presence of the chlorophyll on the photocatalyst increased in general the light absorption and the photocurrent. Overall, our work demonstrated that making composites with recycled plastic bottle caps is a feasible alternative to remove dyes from contaminated drinking water with high efficiency and low cost.

Upcycling discarded cellulosic surgical masks into catalytically active freestanding materials

ABSTRACT

The COVID-19 pandemic outbreak has resulted in the massive fabrication of disposable surgical masks. As the accumulation of discarded face masks represents a booming threat to the environment, here we propose a solution to reuse and upcycle surgical masks according to one of the cornerstones of the circular economy. Specifically, the non-woven cellulosic layer of the masks is used as an environmentally sustainable and highly porous solid support for the controlled deposition of catalytically active metal-oxide nanoparticles. The native cellulosic fibers from the surgical masks are decorated by titanium dioxide (TiO₂), iron oxide (Fe_xO_y), and cobalt oxide (CoO_x) nanoparticles following a simple and scalable approach. The abundant surface -OH groups of cellulose enable the controlled deposition of metal-oxide nanoparticles that are photocatalytically active or shown enzyme-mimetic activities. Importantly, the hydrophilic highly porous character of the cellulosic non-woven offers higher accessibility of the pollutant to the catalytically active surfaces and high retention in its interior. As a result, good catalytic activities with long-term stability and reusability are achieved. Additionally, developed free-standing hybrids avoid undesired media contamination effects originating from the release of nanoscale particles. The upcycling of discarded cellulosic materials, such as the ones of masks, into high-added-value catalytic materials, results an efficient approach to lessen the waste´s hazards of plastics while enhancing their functionality. Interestingly, this procedure can be extended to the upcycling of other systems (cellulosic or not), opening the path to greener manufacturing approaches of catalytic materials.

GRAPHICAL ABSTRACT

A novel approach to upcycle discarded cellulosic surgical masks is proposed, providing a solution to reduce the undesired accumulation of discarded face masks originating from the COVID-19 pandemic. The non-woven cellulosic layer formed by fibers is used as solid support for the controlled deposition of catalytically active titanium dioxide (TiO₂), iron oxide (Fe_xO_y), and cobalt oxide (CoO_x) nanoparticles. Cellulosic porous materials are proven useful for the photocatalytic decomposition of organic dyes, while their peroxidase-like activity opens the door to advanced applications such as electrochemical sensors. The upcycling of cellulose nonwoven fabrics into value-added catalytic materials lessens the waste´s hazards of discarded materials while enhancing their functionality.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-022-04441-9.

A novel S-scheme heterojunction based on 0D/3D CeO2/Bi2O2CO3 for photocatalytic degradation of organic pollutants

A distinct S-scheme heterojunction of 0D/3D CeO2/Bi2O2CO3 photocatalyst was successfully synthesized via hydrothermal method employing for photocatalytic degradation of methylene blue (MB), tetracycline (TC) and aureomycin (AM). Compared with bare...

Controlling morphology evolution of titanium oxide-gold nanourchin for photocatalytic degradation of dyes and photoinactivation of bacteria in the infected wound

We report a one-pot, room-temperature, morphology-controlled synthesis of titanium oxide (TiO_x)-gold nanocomposites (TiO_x-Au NCs) using HAuCl₄ and TiCl₃ as precursors, and catechin as reducing agent. TiO_x-Au NCs have a range of morphologies from star-like to urchin-like shape depending on the concentration of TiCl₃ in the reaction mixture. The urchin-shaped TiO_x-Au NCs exhibited excellent photocatalytic activity toward dye degradation due to strong light absorption, plasmon-induced excitation, high conductivity of the gold, and reduced hole-electron pair recombination. TiO_x-Au NCs have the advantage of a wide range of light absorption and surface plasmon absorption-mediated excitation due to their abundant gold spikes, which enabled the degradation of dyes over 97% in 60 min, using a xenon lamp as a light source. In addition, TiO_x-Au NCs are highly efficient for the photoinactivation of Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA), and Candida albicans through the photodynamic generation of reactive oxygen species (ROS) and damage to the bacterial membrane. The catechin derivatives on the NCs effectively promoted curing MRSA infected wounds in rats through inducing collagen synthesis, migration of keratinocytes, and neovascularization.

Porous Silica Microspheres with Immobilized Titania Nanoparticles for In-Flow Solar-Driven Purification of Wastewater

In this paper, inorganic silica microspheres with interconnected macroporosity are tested as a platform for designing robust and efficient photocatalytic systems for a continuous flow reactor, enabling a low cost and straightforward purification of wastewater through solar-driven photocatalysis. The photocatalytically active microspheres are prepared by wet impregnation of porous silica scaffolds with Trizma-functionalized anatase titania (TiO2) nanoparticles (NPs). NPs loading of 22 wt% is obtained in the form of a thin and well-attached layer, covering the external surface of the microspheres as well as the internal surface of the pores. The TiO2 loading leads to an increase of the specific surface area by 26%, without impacting the typically interconnected macroporosity (≈60%) of the microspheres, which is essential for an efficient flow of the pollutant solution during the photocatalytic tests. These are carried out in a liquid medium for the decomposition of methyl orange and paracetamol. In addition to photocatalytic activity under continuous flow, the microspheres offer the advantage that they can be easily removed from the reaction medium, which is an appealing aspect for industrial applications. In this work, the typical issues of TiO2 NPs photocatalysts are circumvented, without the need for elaborate chemistries, and for low availability and expensive raw materials.

Fast and efficient degradation of water pollutant dyes and fungicide by novel sulfur-doped graphene oxide-modified Ag3PO4 nanocomposite

The sulfur-doped graphene oxide (sGO)-integrated Ag₃PO₄ composite displayed very high catalytic activity toward prominent water pollutants like textile dyes and fungicide under sunlight. The optimum amount of sGO doping was found as 5% for degradation. The novel composite degraded 99% of methylene blue (MB) in only 5 min of sunlight exposure, which is 16 and 8 times faster than Ag₃PO₄ and 5% GO-Ag₃PO₄. High mineralization was observed for MB with a total organic carbon (TOC) removal of 98% in 30 min. The composite mineralized rhodamine B, methyl orange, and acid red 18 dyes with a TOC removal above 95%. Moreover, a toxic dithiocarbamate fungicide thiram was degraded in 1 h with a TOC removal of 82% leaving less toxic thiourea. The formation of sGO-Ag₃PO₄ n-n heterojunction increases charge transport and photocatalytic activity of the composite to incredible extent along with hollow morphology and in situ formed Ag nanoparticles (AgNPs).

Optimization of photocatalytic degradation of rhodamine B using Box-Behnken experimental design: Mineralization and mechanism

The aim of this work was to optimize the photocatalytic degradation of rhodamine B (RhB) using a four-factor Box-Behnken experimental design, and the study was carried out under artificial irradiation (24-W UV lamp) using ZnO in suspension. The Box-Behnken model has been validated with an error less than 5%. A total (100%) RhB removal and COD abatement rates were reached under optimal conditions of treatment time, ZnO dose, and stirring speed at different concentrations of dye. The study of the effect of irradiation type (solar and UV lamp) on the degradation of RhB showed that solar irradiation gave a better rate of degradation with complete discoloration after 2 hr. The study of RhB degradation mechanism indicates that O 2 ∙ - were the main active species for the degradation of this pollutant. The comparison between the degradation of RhB alone and RhB prepared with varnish (as it is usually used in industry) revealed that degradation of RhB alone is faster comparing than that of RhB/varnish mixture. The results showed that the biodegradability was improved after a contact time of 60 min with a BOD₅ /COD ratio increasing from 0.23 to 0.90. PRACTITIONER POINTS: Optimization of the photocatalytic degradation of rhodamine B using a four-factor Box-Behnken experimental design. Investigation of dye mineralization. The degradation mechanism of rhodamine. Biodegradability assessment based on the BOD₅ /COD ratio.

Honeycombed Au@C-TiO2-Xcatalysts for enhanced photocatalytic mineralization of Acid red 3R under visible light

The mineralization of organic pollutants under visible light is challenging, limiting the practical application of photocatalytic technology in wastewater treatment. To achieve the efficient mineralization of Acid red 3R (AR3R), a series of honeycombed catalysts (TiO₂, C-TiO_2-X, Au@TiO₂ and Au@C-TiO_2-X) were prepared via a facile in situ synthetic method and characterized by XRD, TEM, BET, XPS and DRS, respectively. The introduction of C and Au species promote the simultaneous generation of •O₂^- and •OH over Au@C-TiO_2-X under visible light radiation. The Au@C-TiO_2-X catalyst showed superior performance for the deep mineralization of AR3R, affording a TOC removal rate larger than 90 % within 240 min under visible light (> 420 nm). The photocatalytic degradation mechanism of AR3R is proposed according to UV-vis and in situ DRIFTS analysis. The superior photocatalytic activity of Au@C-TiO_2-X is attributed to the synergistic effect of •O₂^- and •OH owing to C doping and Au deposition.

Advances in Template Prepared Nano-Oxides and their Applications: Polluted Water Treatment, Energy, Sensing and Biomedical Drug Delivery

The nano-oxide materials with special structures prepared by template methods have a good dispersion, regular structures and high specific surface areas. Therefore, in some areas, improved properties are observed than conventional bulk oxide materials. For example, in the treatment of dye wastewater, the treatment efficiency of adsorbents and catalytic materials prepared by template method was about 30 % or even higher than that of conventional samples. This review mainly focuses on the progress of inorganic, organic and biological templates in the preparation of micro- and nano- oxide materials with special morphologies, and the roles of the prepared materials as adsorbents and photocatalysts in dye wastewater treatment. The characteristics and advantages of inorganic, organic and biological template are also summarized. In addition, the applications of template method prepared oxides in the field of sensors, drug carrier, energy materials and other fields are briefly discussed with detailed examples.

Porous NiFe-oxide nanocubes derived from prussian blue analogue as efficient adsorbents for the removal of toxic metal ions and organic dyes

A novel porous NiFe-oxide nanocubes (NiFe NCs) binary material was successfully fabricated via a facile and scalable tactic, which involved a morphology-inherited heat treating of Ni₃[Fe(CN)₆]₂·xH₂O prussian blue analogue nanocubes as self-sacrificial templates. Consequently, it was demonstrated that the NiFe NCs consisted of primary nanostructure units and interconnected pores, with an average size of ˜80 nm. When employed as adsorbents, the as-prepared NiFe NCs displayed remarkable adsorption capacities for heavy metal ions (232.3 mg g^-1 for As(V) and 350.71 mg g^-1 for Cr(VI)) and organic dyes (284.99 mg g^-1 for XO and 31.97 mg g^-1 for CR at 298 K). The resulting NiFe NCs further revealed efficient regeneration and reusability even after five consecutive adsorption/desorption cycles. The microscopic spectrum analysis demonstrated that the interaction between As(V) and NiFe NCs was mainly ascribed to the metal-oxide bonds (MO) and hydroxyl groups (OH), while Cr(VI) adsorption was in conjunction with the reduction reaction of Cr(VI) to Cr(III). Furthermore, the adsorption of organic dyes on NiFe NCs depended on the pore structure and molecule sizes of the organic dye molecules. These findings make cost-efficient NiFe NCs materials a powerful candidate for remediating water contaminated with inorganic and organic contaminants.

Activation of fulvic acid-like in paper mill effluents using H2O2/TiO2 catalytic oxidation: Characterization and salt stress bioassays

Increasing environmental concerns about organic waste in paper mill effluents demand alternative wastewater management technology. We reported novel activation of fulvic acid-like in paper mill effluents using hydrogen peroxide (H₂O₂) as oxidizer and titanium oxide (TiO₂) as catalyst. Spectroscopic characteristics of fulvic acid-like in paper mill effluents before and after activation (PFA and PFA-Os, respectively) were compared with a benchmark fulvic acid extracted from leonardite (LFA). Results indicated that PFA-Os exhibited less lignin structures, more functional groups and lower molecular weight than PFA, sharing much similarity with LFA. Among PFA-Os with varying degrees of oxidation, PFA-O-3 activated with 1:2 vol ratio of paper mill effluent and 30% H₂O₂ for 20 min digestion at 90 °C stands out to be the optimal for further examination of its biological activity. Bioassays with rice seed/seedling indicated that applications of LFA at 2-5 mg-C/L and PFA-O-3 at 60-100 mg-C/L significantly increased rice seed germination rate and seedling growth under salt stress imposed with 100 mM NaCl. The mechanism was mainly through reduced oxidative damage via activation of antioxidative enzymes and lipid peroxidation. This study provides the needed technical basis of safer and cleaner technologies for innovative management of paper mill effluents.