A p-n junction NiO-CdS nanoparticles with enhanced photocatalytic activity: A response surface methodology study

Preparation and characterization of cellulose-chitosan/β-FeOOH composite hydrogels for adsorption and photocatalytic degradation of methyl orange

Biopolymer-based hydrogels have received great attention in wastewater treatment due to their excellent properties, e.g., high adsorption capacity, fast kinetics, reusability and ease of operation. In the present work, cellulose-chitosan/β-FeOOH composite hydrogels were prepared via co-dissolution and regeneration process as well as hydrothermal in situ synthesis of β-FeOOH. Effect of β-FeOOH loading on the properties of the composite hydrogels and the removal efficiency of methyl orange (MO) was investigated. Results showed that β-FeOOH was uniformly loaded onto the hydrogel framework, and the nanoporous structure of composite hydrogels could increase not only the effective contact area between β-FeOOH and the pollutants but also the active sites. Moreover, the increased β-FeOOH loading led to the enhanced MO removal rate under light conditions. When the loading time was extended from 6 h to 9 h, the MO removal rate increased by 21%, which can be mainly due to the photocatalytic degradation. In addition, MO removal rate reached 97.75% within 40 min under optimal conditions and attained 80.81% after five repetitions. The trapping experiment and EPR results indicated that the main active species were hydrogel radicals and holes. Consequently, this work provides an effective preparation approach for cellulose-chitosan/β-FeOOH composite hydrogel with high adsorption and photocatalytic degradation, which would hold great promise for wastewater treatment applications.

Photocatalytic degradation of Acid Red 18 by synthesized AgCoFe2O4@Ch/AC: Recyclable, environmentally friendly, chemically stable, and cost-effective magnetic nano hybrid catalyst

Chitosan (Ch) is a linear biodegradable natural carbohydrate polymer and the most appealing biopolymer, such as low-cost biodegradability, biocompatibility, hydrophilicity, and non-toxicity. In this case, Ch was utilized to synthesize AgCoFe2O4@Ch/Activated Carbon (AC) by the modified microwave-assisted co-precipitation method. The physical and chemical structure of magnetic nanocomposites was analyzed and characterized by Field Emission Scanning Electron Microscope (FESEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy Dispersive Spectroscopy (EDS), Diffuse Reflection Spectroscopy (DRS), Value stream mapping (VSM), Fourier transform spectroscopy (FTIR) and BET. The effects of various parameters on the removal of dye (Acid Red18), including catalyst dose, dye concentration, pH, and time were studied. Results showed that the highest removal efficiencies were 96.68 % and 84 % for the synthetic sample and actual wastewater, respectively, in optimal conditions (pH: 3, the initial dye concentration: 10 mgL-1, the catalyst dose: 0.14 gL-1, time: 50 min). Mineralization, according to the COD analysis, was 89.56 %. Photocatalytic degradation kinetics of Acid Red 18 followed pseudo-first order and Langmuir-Hinshelwood with constants of kc = 0.12 mg L-1 min-1 and KL-H = 0.115 Lmg-1. Synthesized photocatalytic AgCoFe2O4@Ch/AC showed high stability and after five recycling cycles was able to remove the pollutant with an efficiency of 85.6 %. So, the synthesized heterogenous magnetic nanocatalyst AgCoFe2O4@Ch/AC was easily recycled from aqueous solutions and it can be used in the removal of dyes from industries with high efficiency.

Influence of Cu-ion doping in NiO NPs and their structural, morphological, optical and magnetic behaviors for optoelectronic devices and magnetic applications

NiO and Cu-ion doped NiO nanoparticles with various concentrations (0.01-0.04 M) have been effectively synthesized in the current investigation using chemical precipitation method. The following techniques were used to characterized the materials' structural, morphological, elemental analysis, functional group, optical and magnetic properties: XRD, TEM, HR-TEM, SAED, SEM, EDX, FTIR, UV, PL and VSM. According to this Scherrer formula, the average crystalline sizes of the materials of pure NiO and Cu-doped NiO were determined to be 16.37 nm, 15.21 nm, 14.88 nm, 18.35 nm, and 10.88 nm, respectively. The HR-TEM images revealed that the d-spacing values about 0.24 nm, which coincides with the (111) plane of cubic NiO for pure and copper doped NiO nanoparticles. The SEM micrographs of Cu-doped NiO nanomaterials shows tiny agglomerated particles, while that of pure NiO nanoparticles shows spherical structure. Pure NiO and Cu-doped NiO nanoparticles have band gap values of 2.32 eV, 2.29 eV, 2.24 eV, 2.22 eV, and 2.27 eV, respectively. The Cu-doped NiO nanoparticles (0.01-0.03 M) at various concentrations can significantly reduce the band gap without significantly altering the structure, making them a potential material for creating optoelectronic devices. Copper was incorporated into NiO nanoparticles, which had a significant impact on the magnetic properties and changed the material from weakly ferromagnetic to ferromagnetic. In comparison to undoped NiO nanoparticles, the saturation magnetization and coercivity values of the 0.01 M and 0.03 M of Cu-doped nanoparticles is much higher. This outcome demonstrates that such Cu-doped NiO nanoparticles have promising magnetic applications.

One-Pot Synthesis of N-Doped NiO for Enhanced Photocatalytic CO2 Reduction with Efficient Charge Transfer

The green and clean sunlight-driven catalytic conversion of CO₂ into high-value-added chemicals can simultaneously solve the greenhouse effect and energy problems. The controllable preparation of semiconductor catalyst materials and the study of refined structures are of great significance for the in-depth understanding of solar-energy-conversion technology. In this study, we prepared nitrogen-doped NiO semiconductors using a one-pot molten-salt method. The research shows that the molten-salt system made NiO change from p-type to n-type. In addition, nitrogen doping enhanced the adsorption of CO₂ on NiO and increased the separation of photogenerated carriers on the NiO. It synergistically optimized the CO₂-reduction system and achieved highly active and selective CO₂ photoreduction. The CO yield on the optimal nitrogen-doped photocatalyst was 235 μmol·g^-1·h^-1 (selectivity 98%), which was 16.8 times that of the p-type NiO and 2.4 times that of the n-type NiO. This can be attributed to the fact that the nitrogen doping enhanced the oxygen vacancies of the NiOs and their ability to adsorb and activate CO₂ molecules. Photoelectrochemical characterization also confirmed that the nitrogen-doped NiO had excellent electron -transfer and separation properties. This study provides a reference for improving NiO-based semiconductors for photocatalytic CO₂ reduction.

Constructing a metal-free 2D covalent organic framework for visible-light-driven photocatalytic reduction of CO2: a sustainable strategy for atmospheric CO2 utilization

A 2D polyimide-linked covalent organic framework (COF) with band gap energy of 2.2 eV is developed as a stable and efficient porous photocatalyst which shows CO2 reduction to formic acid, formaldehyde and methanol.

Synthesis and characterization of SSM@NiO/TiO2 p-n junction catalyst for bisphenol a degradation

Photocatalyst immobilization on support materials is essential for large-scale applications. Here, we describe growth of a p-n junction catalyst (NiO/TiO₂) on a stainless-steel mesh (SSM) support using a facile hydrothermal method. The morphological superiority of the composite over previously reported NiO/TiO₂ catalysts was probed using scanning and transmission electron microscopy. Flower petal-like NiO grew uniformly on SSM, which was evenly covered by TiO₂ nanoparticles. Theoretical and experimental X-ray diffraction patterns were compared to analyze the development of the composite during various stages of synthesis. The photocatalytic activity of a powdered catalyst and SSM@catalyst was compared by measuring bisphenol A (BPA) degradation. SSM@NiO/TiO₂ achieved the highest rate of BPA degradation, removing 96% of the BPA in 120 min. Scavenging experiments were used to investigate the charge separation and degradation mechanism. SSM@NiO/TiO₂ showed excellent reusability potential, achieving and sustaining 91% BPA removal after 10 rounds of cyclic degradation. Reusability performance, composite resilience, apparent quantum yields, and figures of merit suggest that SSM@NiO/TiO₂ has excellent utility for practical applications.

A statistical modeling-optimization approach for photocatalytic degradation of diflouro triazole acetophenone using Ag-Fe co-doped TiO2: response surface methodology

In this research, the performance of Ag-Fe co-doped TiO₂ (Ag-Fe CT) nanophotocatalyst for degradation of diflouro triazole acetophenone (DTA) from aqueous solutions under solar and UV radiations was compared. The novel photocatalyst was synthesized using a sol-gel method with varying Ti to Ag mole ratio (10, 25, 30, 40, 55). Synthetic wastewater was prepared from diflouro triazole acetophenone (DTA concentration 8 g/L and COD = 75,000 mg/L). Ag-Fe CT 30 photocatalyst has shown maximum COD removal efficiency for solar and UV irradiation. Ag-Fe CT 30 photocatalyst was able to absorb visible and UV radiations. Recyclability test proved that Ag-Fe CT 30 can be reused 3 times effectively for a not significant decrease in COD removal efficiency. A response surface methodology (RSM) was used to study the single and combined effects of pH, photocatalyst dose, and Ti to Ag mole ratio parameters. Model showing relation of parameters with COD reduction efficiency has been developed and optimization has been carried out for solar and UV radiations. Results revealed that the optimal conditions for DTA removal were initial pH 5, photocatalyst dose of 3 g/L, and Ti to Ag mole ratio of 30. Maximum COD removal efficiency of 76% and 86% was observed under solar and UV radiations, respectively. This study would be useful for the removal of non-biodegradable organics from high-strength COD effluent in an economical and eco-friendly way.

Electrospun 1D-NiO hollow nanowires on glass support for the sunlight-driven photodegradation of methylene blue

Sunlight-driven semiconductor photocatalysts have received substantial attention due to environmental degradation, but a simple and reusable photocatalyst design has been a challenging task. Herein, we report the fabrication of a one-dimensional hollow semiconducting nanowire structure by electrospun-mediated nickel oxide nanowires (NiO NWs) as a reusable photocatalyst by direct deposition on glass substrates. The effective control of the sunlight-driven hollow nanowires as the photocatalyst has a high surface area for multiple light-harvesting and interface redox reactions, a nanostructured thin shell for accelerated charge separation, transportation, and a large length-diameter ratio for easy recycling. The electrospun NiO NWs were nest-like hollow nanostructure fibers, crystalline, and with a high density, and the synthesis and parameters were thoroughly investigated to achieve the characteristic shape of the hollow NiO NWs. Further, the photocatalytic activity of the NiO NWs on glass substrates for the selective breakdown of methylene blue (MB) under sunlight irradiation to optimize the efficiency of the NiO NWs, such as degradation techniques, concentration, and pH of the MB solution. The stability and reusability of the NiO NWs were tested successfully in several reusable cycles, with only a 2% degradation difference. The reaction rate was found to be 0.054 min⁻¹ for MB (5 μM) and 0.033 min⁻¹ for MB (10 μM) at pH 11 for 60 min, and the higher activity parameter was calculated to be 3.3 × 10⁻³ min⁻¹ mg⁻¹ L⁻¹ due to their hollow structure and effective area of the NiO NWs. They contain more superficially-entrapped holes that change with chemisorbed oxyhydroxyl OH or H₂O to form OH⁻ radicals. The specific active hollow surface area rises, whereas the rate of optical-electronic hole recombination drops. The photocatalytic degradation performance of the fabricated one-step electrospun hollow NiO NW-based photocatalyst on substrates showed speed, reusability, and promoted the formation of radicals capable of decomposing organic pollutants, which were shown to have application in photocatalysis.

One-step fabrication of hollow NiO NWs photocatalyst on glass substrate by electrospun then tested for their capacity to break down MB in solutions exposed to sunlight.

Quantum-dot sensitized hierarchical NiO p–n heterojunction for effective photocatalytic performance

A facile and low-cost pseudo successive ionic layer adsorption and reaction technique was used to deposit cadmium sulfide quantum dots (CdS QDs) on hierarchical nanoflower NiO to form effective and intimate NiO/CdS, p–n heterojunctions.

The photocatalytic rate of ZnO supported onto natural zeolite nanoparticles in the photodegradation of an aromatic amine

Aniline and its derivate are critical environmental pollutants, and thus, the introduction of an eco-friendly catalyst for removing them is an important research future. The ZnO supported on the ball-mill prepared clinoptilolite nanoparticles (CNPs) was prepared via an ion-exchange process followed by the calcination process. The amount of loaded ZnO in the ZnO-CNP (CZ) samples varied as 0.54, 0.63, 0.72, and 0.86 meq/g as the Zn(II) concentration in the ion-exchange solution varied from 0.1 to 0.5 M. The ZnO-CNP catalyst was briefly characterized by XRD, FTIR, and DRS techniques. The pHpzc value for the various ZnO-CNPs was about 7.1 that had no change with the ZnO loading. By applying the Scherrer equation on the XRD results, a nano-dimension of about 50 nm was obtained for the catalyst. Bandgap energy of the ZnO-CNP samples was estimated by applying the Kubelka-Munk equation on the DRS reflectance spectra. The value for the CZ2 catalyst was about 3.64 eV. The supported ZnO-CNP sample was then used in the photodegradation of 2,4-dichloroaniline (DCA). Raw zeolite showed a relatively low photocatalytic activity. The degradation efficiency was followed by recording the absorbance of the DCA solution by UV-Vis spectrophotometer. The effects of the essential critical operating factors on the degradation efficiency were kinetically studied by applying the Hinshelwood equation to the results. The ZnO-CNP catalyst with 2 w% ZnO showed the best photocatalytic rate in the optimal conditions of 0.75 g/L, C_DCA: 15 ppm, and the initial pH: 5.8. Finally, HPLC analysis of the blank and the photodegraded DCA solutions at 180 and 300 min confirmed 74 and 87% of DCA molecules were degraded during these times. The results confirm that supported ZnO onto clinoptilolite caused enhanced photocatalytic activity because the zeolite internal electrical field prevents the e^-/h⁺ recombination.

Photocatalytic degradation of tetracycline antibiotics using delafossite silver ferrite-based Z-scheme photocatalyst: Pathways and mechanism insight

Tetracycline (TC), a widely used antibiotic, is easy to enter the aquatic ecosystem through soil erosion, livestock manure and wastewater discharge, resulting in a series of risks. The application of Z-scheme photocatalysts with efficient interface charge separation and transfer has been regard as an effective strategy for antibiotic degradation. Herein, a novel ternary Z-scheme Bi₁₂O₁₇Cl₂/Ag/AgFeO₂ was successfully synthesized by ultrasound-assisted ethanol reduction of Ag⁺ on the interface of Bi₁₂O₁₇Cl₂ and AgFeO₂. The Bi₁₂O₁₇Cl₂/Ag/AgFeO₂ Z-scheme system exhibited an enhanced photocatalytic degradation capability for TC, which was over 6.5 times and 2.4 times higher than those of AgFeO₂ and Bi₁₂O₁₇Cl₂/AgFeO₂ system, respectively. The photocatalytic process of TC was explored, and the results indicated that an optimum catalyst concentration of 0.5 g L^-1 and a primeval pH (without adjustment) favored the degradation process, while the introduction of exogenous anions (CO₃^2-, SO₄^2- and NO₃^-) and organic matter (HA) supressed the degradation of TC. Simultaneously, the possible pathway for the degradation process of TC was presented based on the liquid chromatography-mass spectrometry (LC-MS) analysis. Active species trapping experiments and ESR spectra revealed the significant contribution of O₂^- in the TC degradation, and verified the Z-scheme mechanism of the Bi₁₂O₁₇Cl₂/Ag/AgFeO₂ system.

Lanthanum ions decorated 2-dimensional g-C3N4 for ciprofloxacin photodegradation

The low band gap energy and high surface area two-dimensional materials allow it to tune its basic properties using surface decoration. Here, La³⁺ are decorated on two-dimensional graphitic carbon nitride using a simple and easily scalable chemisorption process with an adsorption capacity of 657.32 mg g^-1. In the X-ray diffraction (XRD) study, the positive slope of the W-H plot elucidates the tensile strain generation (0.103) in La³⁺ ions decorated 2D-g-C₃N₄ (La³⁺-2D-g-C₃N₄). The high-resolution transmission electron microscope (HR-TEM) study and the higher I_D/I_G ratio (0.82) in the Raman spectroscopy study confirm the more defects intensification in La³⁺-2D-g-C₃N₄. The reduction in band gap energy for La³⁺-2D-g-C₃N₄ (from 2.83 eV to 2.21 eV) has shown a good correspondence with the band structures study as obtained from the DFT study. In the DFT study, the significant contributions of N atoms in charge transfer validate the N 1s findings from the X-ray photoelectron spectroscopy (XPS) study for La³⁺-2D-g-C₃N₄. La³⁺-2D-g-C₃N₄ shows the photodegradation efficiency (93%) of ciprofloxacin under UV irradiation, which is superior to pristine 2D-g-C₃N₄ (82%) as well as other g-C₃N₄ based nanocatalysts. Also, La³⁺ decoration results in enhancement (32.3%) in photodegradation kinetics rate. The degradation and kinetics studies in the presence of different scavengers ensure that the O₂- and OH^- radicals are mostly responsible for the ciprofloxacin photodegradation. The Liquid chromatographic-mass spectroscopy and the high-performance liquid chromatography studies confirm the photodegradation. The reusability of La³⁺-2D-g-C₃N₄ is tested up to the fifth cycle. FTIR and UV-visible absorption spectroscopy confirm the stability of the used photocatalyst.

Efficient removal of Pb(II) ions from aqueous solution by modified red mud

In the work, we employed a hydrothermal method for modification of red mud using colloidal silica and sodium hydroxide under mild conditions, and applied it into adsorbing Pb(II) ions in aqueous solutions. In the modification, zeolite structure was formed. The adsorption experiments found that the adsorption capacity of the modified red mud for Pb(II) ions was significantly improved, almost 10 times as much as that of the original red mud. Both the pseudo-first-order and pseudo-second-order kinetic equation can describe the adsorption process, indicating it a more complicated interaction. Langmuir and Dubinin-Radushkevich models well fit the adsorption isotherm, indicating that the modified red mud mainly removes lead ions from aqueous solution by monolayer physical adsorption. According to the fitting results, the saturated adsorption capacity of Pb (II) by the modified red mud is 551.11 mg/g, confirming its high efficiency adsorption performance. XRD, FTIR, XPS and SEM-EDS all detected the formation of PbCO₃ and Pb₃(CO₃)₂(OH)₂. It was speculated that the adsorption mechanism should be attributed to the joint contribution of ion exchange and precipitation. The excellent performance of the modified red mud on Pb(II) ions adsorption makes it a promising candidate for the treatment of wastewater contaminated by heavy metal ions.

Cadmium sulfide quantum dots/dodecahedral polyoxometalates/oxygen-doped mesoporous graphite carbon nitride with Z-scheme and Type-II as tandem heterojunctions for boosting visible-light-driven photocatalytic performance

It is known that fabrication of tandem heterojunctions between different types of heterojunctions can promote the charge separation. Herein, novel cadmium sulfide quantum dots (CdS QDs)/dodecahedral phosphotungstic acid potassium K₃PW₁₂O₄₀ (KPW)/oxygen-doped mesoporous graphite carbon nitride (meso-g-C₃N₄) nanosheets tandem heterojunctions are prepared by the hydrothermal method combined with direct template calcination and in-situ chemical sedimentation strategy. The results show that tandem heterojunctions formed by the Z-Scheme heterojunction between CdS QDs and KPW and the type-II heterojunction between CdS QDs and meso-g-C₃N₄ can extend the optical response into visible light region. Importantly, under visible light irradiation, photocatalytic hydrogen production rate and photocatalytic Cr⁶⁺ removal rate over CdS/KPW/meso-g-C₃N₄ is higher than that of KPW and CdS/KPW. This remarkable photocatalytic performance is due to the effective charge separation and transfer of the special tandem heterojunction structure. This novel tandem heterojunction will offer new insights for fabricating other high-performance photocatalytic systems.

Hydrothermal synthesis of novel 1-aminoperylene diimide/TiO2/MoS2 composite with enhanced photocatalytic activity

1-aminoperylene diimide/TiO2/MoS2 composite (NH2-PDI/TiO2/MoS2) with ordered structure was prepared by hydrothermal synthesis method. The composite was characterized by XRD, SEM, FTIR, XPS, BET, DRS, PL, EIS, Raman, photocurrent, and Mott-Schottky plots spectroscopy. The potential positions of the conduction and valence bands, and the band gap energy of the semiconductors were estimated. The composite exhibited higher photocatalytic activity compared with the mono-component systems. The apparent rate constants (k) were determined as 0.00616, 0.00352, 0.00738, 0.00517, 0.00752, and 0.00806 min-1 for TiO2, NH2-PDI, NH2-PDI/TiO2, MoS2, MoS2/TiO2, and NH2-PDI/TiO2/MoS2, respectively. The detection of radical scavengers confirmed that superoxide radicals, photogenerated holes, and photogenerated electrons were the main active substances for MB degradation. Between type II- heterojunction mechanism and Z-scheme mechanism, the latter could explain the enhanced photocatalytic activity of the composite better. The Z-scheme mechanism accumulates more electrons at CB level of NH2-PDI and hence generates more super oxide radicals.

Fabrication of Dandelion-like p-p Type Heterostructure of Ag2O@CoO for Bifunctional Photoelectrocatalytic Performance

A novel three-dimensional purple dandelion-like hierarchical Ag₂O@CoO heterojunction with an appropriate redox potential was constructed by chemical precipitation of Ag₂O nanoparticle on flower-like CoO. By feat of this hierarchical structure, the Ag₂O@CoO photocathode showed significantly high photoelectroreduction activities toward p-nitrophenol (p-NP) and Cr(VI). The high performance of Ag₂O@CoO was mainly attributed to the specific structural characteristics and synergistic effect of each chemical component. This hierarchical structure could effectively increase the specific surface area, provide more exposed active edges, and be beneficial for multiple light reflection/scattering channels and light utilization efficiency. The introduction of Ag₂O optimized the composition and further improved the band structure, resulting in an improved separation of photogenerated electrons and holes. The unique photocathode achieves a removal efficiency of 86% for photoelectrocatalytic p-NP degradation after 120 min and 95% for Cr(VI) after 40 min under visible light irradiation with excellent stability. This research provided a simple way for the synthesis of photoelectrocatalytic material with potential applications in the field of environmental governance with visible light illumination.

Full use of factors promoting catalytic performance of chitosan supported manganese porphyrin

In order to make full use of the impact of internal and external factors on the performance of title catalyst for ethyl benzene oxidation, the key internal influencing factors on the catalytic performance were modulated by coordinating and grafting manganese porphyrin to mesoporous and macroporous chitosan, and the important external factors (i.e. oxidation reaction conditions) were optimized using Response Surface Methodology. Under the Response Surface Methodology optimized oxidation reaction conditions (176.56 °C, 0.59 MPa, and 0.25 mg amount of manganese porphyrin), the catalyst could be used at least five times. The ethyl benzene conversion, catalyst turnover numbers, and yields reached up to 51.2%, 4.37 × 106 and 36.4% in average, respectively. Compared with the other optimized oxidation reaction conditions, the corresponding values increased 17%, 26% and 53%. Relative to the manganese porphyrin, the catalytic performance and efficiency of the immobilized catalyst had notably increased.

Tragacanth-mediate synthesis of NiO nanosheets for cytotoxicity and photocatalytic degradation of organic dyes

In this study, NiO nanosheets have been manufactured using a co-precipitation approach that involved the usage of nickel nitrate (Ni (NO₃)₂.6H₂O) as the raw material and tragacanth in the role of a stabilizing agent. NiO nanosheets have been fabricated through the reduction of nickel nitrate solution that had been obtained by the application of aqueous extract of tragacanth, which is capable of functioning as a reducing and stabilizing agent. In the following, the physical and chemical properties of tragacanth-stabilized NiO nanosheets have been identified via FESEM, EDS, XRD, UV-Vis, and FT-IR techniques. According to the XRD pattern, these particular nanosheets have contained a cubic structure and group space Fm3m, along with the average size of about 18 to 43 nm that had been in agreement with the FESEM measurements. In addition, we have evaluated the photocatalytic activity of tragacanth-stabilized NiO nanosheets on the degradations of methylene blue (MB) and methyl orange (MO) dyes. The performed photocatalytic assessment has displayed that the nanosheets can degrade 82% of MO within 210 min and 60% of MB in 300 min. The cytotoxicity of tragacanth-stabilized NiO nanosheets on human Glioblastoma cancer (U87MG) cell lines has been investigated via the MTT assay, while it has been detected in the obtained results that the inhibitory concentration (IC₅₀) had been 125 µg/mL.

Chemical reduction of methylene blue in the presence of nanocatalysts: a critical review

Methylene blue (MB) (3,7-bis (dimethylamino)-phenothiazin-5-ium chloride) is a harmful pollutant and has been long been known for its detrimental effects on human health. Over the recent years, many strategies including reduction, oxidation, biological and photochemical degradation have been reported for converting this harmful dye into commercially useful products. Among the aforementioned strategies, the nanocatalytic reduction of MB into its reduced counterpart, i.e. leucomethylene blue, is considered more preferable because it has been reported to have numerous applications in various industrial fields in the academic literature. The reduction of MB is the kinetically unfavorable reaction. Henceforth, various nanocatalytic systems utilizing different kinds of stabilization mediums have reportedly been used for speeding up this particular reaction. This article attempts to not only describe the fundamental properties of the reduction reaction of MB but also present the classification of the recently reported nanocatalytic assemblies on the basis of the utilized supporting medium. Various techniques used for the characterization of nanocatalytic systems reported for the reduction of MB have been summarized in this review. The thermodynamics, kinetics and mechanistic studies of this nanocatalytic reaction have also been narrated here. This critical review has been written comprehensively to abridge the recent research progress in the assemblage of nanocatalytic systems used for the reduction of MB and to propose some new ideas for further development in this area.