Application of visible light on copper-doped titanium dioxide catalyzing degradation of chlorophenols

An Up-to-Date Review on the Remediation of Dyes and Phenolic Compounds from Wastewaters Using Enzymes Immobilized on Emerging and Nanostructured Materials: Promises and Challenges

Addressing the critical issue of water pollution, this review article emphasizes the need to remove hazardous dyes and phenolic compounds from wastewater. These pollutants pose severe risks due to their toxic, mutagenic, and carcinogenic properties. The study explores various techniques for the remediation of organic contaminants from wastewater, including an enzymatic approach. A significant challenge in enzymatic wastewater treatment is the loss of enzyme activity and difficulty in recovery post-treatment. To mitigate these issues, this review examines the strategy of immobilizing enzymes on newly developed nanostructured materials like graphene, carbon nanotubes (CNTs), and metal-organic frameworks (MOFs). These materials offer high surface areas, excellent porosity, and ample anchoring sites for effective enzyme immobilization. The review evaluates recent research on enzyme immobilization on these supports and their applications in biocatalytic nanoparticles. It also analyzes the impact of operational factors (e.g., time, pH, and temperature) on dye and phenolic compound removal from wastewater using these enzymes. Despite promising outcomes, this review acknowledges the challenges for large-scale implementation and offers recommendations for future research to tackle these obstacles. This review concludes by suggesting that enzyme immobilization on these emerging materials could present a sustainable, environmentally friendly solution to the escalating water pollution crisis.

Photoactive Materials for Decomposition of Organic Matter Prior to Water Analysis—A Review Containing Original Research

Water plays a fundamental role in meeting the basic needs of society. Surface waters contain numerous organic pollutants, such as pesticides, drugs, and surfactants. The use of photolysis processes in organic matter degradation not only has practical applications in wastewater treatment but is also of major importance in the pretreatment of samples prior to the trace analysis of numerous analytes. The heterogeneous degradation is simple to implement prior to ultra-traces determination and is the only one allowed before the speciation analysis. Speciation analysis is currently the most important environmental challenge. The analysis of water, including tests associated with wastewater pretreatment and the monitoring of aqueous ecosystems, is the largest segment of environmental analysis. In the trace analysis of water, organic compounds are the principal interfering compounds reducing the quality of the obtained results or even preventing the determination of the examined analytes altogether. Some analytical techniques do not perform well in the presence, for example, of surfactants, so mineralization is sometimes required. Advanced oxidation processes are used to remove interfering organic compounds. The oxidation can be performed using homogenous photolysis (UV mineralization with hydrogen peroxide addition), while heterogenous photolysis using semiconductors helps to increase the removal efficiency of interferents dissolved in water. Utilizing semiconductor nanostructured materials as photocatalysts has been shown to be effective for the adequate removal of a wide spectrum of pollutants in water. Several semiconductor systems are used in the degradation of organic compounds, e.g., TiO2, Fe3O4, WO3, Fe2O3, ZnO, and mixtures of these oxides enriched with various precious metals, such as silver or gold. It is very challenging to manage the selectivity and reduction power so that organic compounds can be degraded but without disturbing the speciation of As, Cr, or Tl. Chemical modification of samples and the selection of semiconductor layers, light wavelength, and pH allow for the targeted degradation of specific compounds but may also indirectly affect the analysis of water samples. This review is a presentation of the state of the art of photocatalysis as a simple and effective technique for sample pretreatment in ultra-trace and speciation analysis and its critical as well as unpublished data related to this topic.

A smart enzyme reactor based on a photo-responsive hydrogel for purifying water from phenol contaminated sources

In this paper, a smart enzyme reactor (SER) was synthesized using immobilized tyrosinase (Tyr) in a photo-responsive hydrogel via a polydopamine-assisted self-assembly strategy for purifying water from phenol contaminated water. PDA was not only utilized as a binder between Tyr and the hydrogel to prevent the leakage of Tyr with relatively high enzymatic activity from the SER, but also acted as a light absorber to trigger the hydrophilic/hydrophobic switching of PNIPAm hydrogels to realize the efficient reclamation of clean water. Experimental results showed that the SER maintained a well-defined porous structure with excellent elasticity, which was beneficial for water transport and enzyme accessibility. And the stability and reusability of Tyr in the degradation of phenol were all improved. Furthermore, clean water could be reclaimed completely and facilely by light irradiation after enzymatic remediation in the SER.

Vanadium selenide decorated reduced graphene oxide nanocomposite: A co-active catalyst for the detection of 2,4,6 - Trichlorophenol

Transition metal chalcogenides (TMCs) have great potential in diverse electrochemical technologies owing to their unique characteristics. In the present work, we portray the design and synthesis of Vanadium selenide (V₂Se₉)/reduced graphene oxide (rGO) forming a two-dimensional (2D) hybrid nanocomposite via a simple hydrothermal method. The successfully synthesized nanocomposite underwent in-depth surface and morphological characterizations by XRD, Raman spectroscopy, XPS, TEM, STEM and its potential as an electro catalyst was investigated by using glassy carbon electrode (GCE) for the detection of 2,4,6-trichlorophenol (TCP). The structural features favored a high charge transfer ratio, high surface area as well as excellent conductivity and catalytic activity. The V₂Se₉/rGO/GCE modified electrode showed a low charge transfer resistance (R_ct) of 54.057 Ω cm², a decent detection limit (LOD) of 35.07 nM and a very high sensitivity of 22 μA μM^-1 cm^-2 in a working range of 0.001 μM-1150 μM. This is due to the active proton interaction, surface enhancement, and positive synergistic effect between rGO and V₂Se₉. The proposed sensor has good detection potential in agricultural soil, river water, fish, and beverage samples like wine and apple juice. The obtained results from our investigation would elucidate the application of the catalyst in electrochemical sensors.

A Review on Metal Ions Modified TiO2 for Photocatalytic Degradation of Organic Pollutants

TiO2 is a semiconductor material with high chemical stability and low toxicity. It is widely used in the fields of catalysis, sensing, hydrogen production, optics and optoelectronics. However, TiO2 photocatalyst is sensitive to ultraviolet (UV) light; this is why its photocatalytic activity and quantum efficiency are reduced. To enhance the photocatalytic efficiency in the visible light range as well as to increase the number of the active sites on the crystal surface or inhibit the recombination rate of photogenerated electron–hole pairs electrons, various metal ions were used to modify TiO2. This review paper comprehensively summarizes the latest progress on the modification of TiO2 photocatalyst by a variety of metal ions. Lastly, the future prospects of the modification of TiO2 as a photocatalyst are proposed.

Nickel ferrite nanoenabled graphene oxide (NiFe2O4@GO) as photoactive nanocomposites for water treatment

Nanocomposite materials can enhance the capabilities of water treatment processes such as photocatalysis. In this work, novel light-driven nanocatalysts were synthesized by using nickel ferrite (NiFe₂O₄) to nanoenable graphene oxide (GO) substrates. GO is an emerging 2D nanomaterial with high conductivity and adsorption properties. Moreover, the electric properties of GO improve photocatalytic performance by promoting charge carrier separation. Results of the characterization of the nickel ferrite nanoenabled graphene oxide (NiFe₂O₄@GO) nanocomposites demonstrate that homogeneous and stable photocatalysts were produced. The as-synthesized nanocatalysts enabled complete decolorization of the colored water matrix in short irradiation times of 150 min using minimal catalyst loading at 0.5 g L^-1. The selective hook and destroy mechanism reduced the competitive effect of co-existing ions in solution. Furthermore, the use of specific scavengers helped to elucidate the degradation mechanisms of organic dye methylene blue by NiFe₂O₄@GO nanocomposites.

Doping TiO2 with CuSO4 enhances visible light photocatalytic activity for organic pollutant degradation

Photocatalysis is one of the most promising advanced oxidation processes due to the capability of solid catalyst to continuously produce oxidant species under light irradiation. The use of conventional UV lamps is high cost intensive, which undermines the possible implementation in developing countries. Visible light active photocatalysts can overcome these challenges and find a market opportunity for competitive technology implementation. This work proposes the synthesis of visible light active catalyst following a facile sol-gel synthesis that introduces CuSO₄ as dopant in TiO₂. Results present complete abatement of methylene blue in 120 min of treatment under 50 mW cm^-2 of blue light (λ = 450 nm), while commercial P25 TiO₂ presented null abatement under identical conditions. Synthesis parameters including dopant level and calcination temperature allowed defining optimum synthesis conditions based on material characteristics modification and catalytic activity enhancement. A doping level of 0.21 mol% CuSO₄ was identified as optimum condition to enable visible light photocatalysis of doped TiO₂ catalysts calcined at 300 °C. Finally, operational parameters were evaluated defining a wide range of pH operation under 3.0 g L^-1 of catalyst dose to treat up to 20 g L^-1 of highly recalcitrant phenothiazine dye. These optimum conditions allowed complete dye removal under visible light after 120 min of treatment.

Enhanced Photocatalytic Activity of Semiconductor Nanocomposites Doped with Ag Nanoclusters Under UV and Visible Light

Emerging contaminants (ECs) represent a wide range of compounds, whose complete elimination from wastewaters by conventional methods is not always guaranteed, posing human and environmental risks. Advanced oxidation processes (AOPs), based on the generation of highly oxidizing species, lead to the degradation of these ECs. In this context, TiO2 and ZnO are the most widely used inorganic photocatalysts, mainly due to their low cost and wide availability. The addition of small amounts of nanoclusters may imply enhanced light absorption and an attenuation effect on the recombination rate of electron/hole pairs, resulting in improved photocatalytic activity. In this work, we propose the use of silver nanoclusters deposited on ZnO nanoparticles (ZnO–Ag), with a view to evaluating their catalytic activity under both ultraviolet A (UVA) and visible light, in order to reduce energetic requirements in prospective applications on a larger scale. The catalysts were produced and then characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD) and inductively coupled plasma-optical emission spectrometry (ICP-OES). As proof of concept of the capacity of photocatalysts doped with nanoclusters, experiments were carried out to remove the azo dye Orange II (OII). The results demonstrated the high photocatalytic efficiency achieved thanks to the incorporation of nanoclusters, especially evident in the experiments performed under white light.

Niobium Oxide Catalysts as Emerging Material for Textile Wastewater Reuse: Photocatalytic Decolorization of Azo Dyes

Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the developing areas of Northeast Brazil, which receives over 22 MJ m2 of natural sunlight irradiation annually. The application of photocatalytic treatment could incentivize water reuse practices in small and mid-sized textile businesses in the region. This work reports the facile synthesis of Nb2O5 catalysts and explores their performance for the treatment of colored azo dye effluents. The high photoactivity of this alternative photocatalyst makes it possible to quickly obtain complete decolorization, in less than 40 min of treatment. The optimal operational conditions are defined as 1.0 g L−1 Nb2O5 loading in slurry, 0.2 M of H2O2, pH 5.0 to treat up to 15 mg L−1 of methyl orange solution. To evaluate reutilization without photocatalytic activity loss, the Nb2O5 was recovered after the experience and reused, showing the same decolorization rate after several cycles. Therefore, Nb2O5 appears to be a promising photocatalytic material with potential applicability in wastewater treatment due to its innocuous character and high stability.

Copper-doped TiO2 photocatalysts: application to drinking water by humic matter degradation

The aim of this study was to determine the photocatalytic performance of copper-doped TiO2 (Cu-TiO2) specimens on the degradation of dissolved organic matter (DOM) represented by a model humic acid (HA). TiO2 was synthesized by sol-gel method from an alkoxide precursor. Cu-doped TiO2 specimens containing 0.25 wt% and 0.50 wt% Cu were prepared by wet impregnation method using sol-gel synthesized as well as bare TiO2 P-25 and characterized by XRD, SEM, XPS, Raman spectroscopy, UV-DRS, and BET measurements. Their photocatalytic activities were evaluated with regard to degradation kinetics of HA in terms of UV-vis and fluorescence spectroscopic parameters and organic contents. HA fluorescence excitation emission matrix (EEM) contour plots indicated that the solar photocatalytic degradation pathway was TiO2-type specific and Cu dopant content.

Photoelectrocatalytic decolorization of azo dyes with nano-composite oxide layers of ZnO nanorods decorated with Ag nanoparticles

Photoelectrocatalysis provides an excellent frame for the application of photocatalytic nanostructured materials on easy recoverable supports. This study reports the two-step synthesis of hierarchically nanostructured ZnO/Ag composite photoelectrodes. Wurtzite ZnO was selectively electronucleated as spheroidal seeds on fluor doped tin oxide substrates and nanodecorated with Ag nanoclusters under electrochemical control. Hierarchically organized nanorods were selectively chemically grown on the plane (002) perpendicular to the substrate from ZnO/Ag seeds. Solutions emulating dye effluents with the usual contents of 0.1 M of NaCl and a model azo dye (Methyl Orange) were decolorized using ZnO/Ag nanorods in different treatments. Photocatalysis attained discrete decolorizations of 8% whereas photoelectrocatalysis completely decolorized solutions after 60 min. The influence of the metal/semiconductor interface (ZnO/Ag) as introduced Schottky barrier is studied demonstrating a four-fold enhancement on decolorization kinetics respect bare ZnO nanorods. The influence of the seed growth control on the final photoelectrocatalytic response is reported to control the hierarchical organization of nanorods. This resulted in different decolorization kinetics as result of the differences on the efficient use of the delivered photons conditioned by the photoelectrode structure.

UV-Vis-Induced Degradation of Phenol over Magnetic Photocatalysts Modified with Pt, Pd, Cu and Au Nanoparticles

The combination of TiO₂ photocatalyst and magnetic oxide nanoparticles enhances the separation and recoverable properties of nanosized TiO₂ photocatalyst. Metal-modified (Me = Pd, Au, Pt, Cu) TiO₂/SiO₂@Fe₃O₄ nanocomposites were prepared by an ultrasonic-assisted sol-gel method. All prepared samples were characterized by X-ray powder diffraction (XRD) analysis, Brunauer-Emmett-Teller (BET) method, X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), Mott-Schottky analysis and photoluminescence spectroscopy (PL). Phenol oxidation pathways of magnetic photocatalysts modified with Pt, Pd, Cu and Au nanoparticles proceeded by generation of reactive oxygen species, which oxidized phenol to benzoquinone, hydroquinone and catechol. Benzoquinone and maleic acid were products, which were determined in the hydroquinone oxidation pathway. The highest mineralization rate was observed for Pd-TiO₂/SiO₂@Fe₃O₄ and Cu-TiO₂/SiO₂@Fe₃O₄ photocatalysts, which produced the highest concentration of catechol during photocatalytic reaction. For Pt-TiO₂/SiO₂@Fe₃O₄ nanocomposite, a lack of catechol after 60 min of irradiation resulted in low mineralization rate (CO₂ formation). It is proposed that the enhanced photocatalytic activity of palladium and copper-modified photocatalysts is related to an increase in the amount of adsorption sites and efficient charge carrier separation, whereas the keto-enol tautomeric equilibrium retards the rate of phenol photomineralization on Au-TiO₂/SiO₂@Fe₃O₄. The magnetization hysteresis loop indicated that the obtained hybrid photocatalyst showed magnetic properties and therefore could be easily separated after treatment process.