Synergistic cobalt oxide/reduced graphene oxide/biochar nano-composite catalyst: harnessing the power of the catalyst for sustainable remediation of organic dyes and chromium(vi)

The exponential growth of industrial activities has led to a significant rise in the release of organic effluents, containing hazardous heavy metals and dyes, into the environment. These pollutants exhibit resistance to conventional biodegradation processes and are associated with carcinogenic properties, posing a severe threat to living organisms. In this context, the present research endeavours to address this environmental challenge through the development of an affordable and efficient photocatalyst, the Co3O4/reduced graphene oxide/biochar (CBG-10) heterostructure. The structural analysis of CBG-10, conducted through various techniques such as XRD, XPS, SEM, and optical property measurements, demonstrates its potential as a highly effective and easily recoverable catalyst for the mineralization of persistent pollutants like methylene blue, malachite green, and hexavalent Cr(vi). The recyclability of CBG-10 was confirmed through XRD studies, highlighting its stability and practical usability in wastewater purification. The photocatalytic behaviour of the catalyst was attributed to the generation of hydroxyl (˙OH) and superoxide radicals (˙O2-) during visible light illumination, as revealed by quenching experiments. The cost-effectiveness and stability of CBG-10 position it as a promising solution for addressing the challenges associated with the removal of stubborn organic contaminants from wastewater, thereby contributing to environmental protection and public health.

Waste-Extracted Zn and Ag Co-Doped Spent Catalyst-Extracted V2O5 for Photocatalytic Degradation of Congo Red Dye: Effect of Metal-Nonmetal Co-Doping

The current study applies the eco-friendly principle of “wastes treat wastes”. By swift methods, a composite photocatalyst was prepared from waste-extracted oxides, namely V2O5, Ag, and ZnO. The metal–lixiviant complexes were used as metal precursors, where the lixiviants act as auto-templates and increase the compatibility between the mixed metallic species, and their controlled thermal removal generates pores. The tri-constitute composite catalyst was doped with nitrogen. The constitution, surface composition, and optical properties of the doped catalysts were investigated by XRD, SEM, TEM, BET surface analysis, XPS, diffuse reflectance, and PL spectra. The as-prepared catalysts were employed in the photodegradation of Congo red dye (CR) under visible irradiation at ambient temperature. The degree of Ag dispersion had a significant effect on the bandgap, as did metal and metal-nonmetal co-doping. The efficiency of dye removal changes dramatically with time up to 120 min, after which it begins to decrease. According to the pH effect, the normal pH of Congo red dye (6.12) is optimal. At a catalyst dose of 1 g L−1 and an irradiation period of 120 min, photodegradation efficiency reached 89.9% and 83.4% over [Ag0.05 ZnO0.05 V2O5(0.90)] and [Ag0.05 ZnO0.05 V2O5(0.90)]N, respectively. The kinetic study depicted the significant role of mass transfer in the reaction rate. The obtained rate constants were 0.995 mole L−1 S−1 and 0.998 mole L−1 S−1 for [Ag0.05 ZnO0.05 V2O5(0.90)] and [Ag0.05 ZnO0.05 V2O5(0.90)]N, respectively.

Photocatalysis: an effective tool for photodegradation of dyes-a review

The disposal of dye-contaminated wastewater is a major concern around the world for which a variety of techniques are used for its treatment. The photocatalytic treatment of dye-contaminated wastewater is one of the treatment methods. Semiconductor-assisted photocatalytic treatment of dye-contaminated wastewater has gained pronounced attention recently. This review outlines the recent advancements in the photocatalytic treatment of dye-contaminated wastewater. The photocatalytic degradation of dyes follows three types of mechanisms: (1) dye sensitization through charge injection, (2) indirect dye degradation through oxidation/reduction, and (3) direct photolysis of dye. Several experimental parameters like initial concentration of dyes, pH, and catalyst dosage significantly affect the photocatalytic degradation of dyes. The photocatalytic materials can be categorized into three generations. The single-component (e.g., ZnO, TiO₂) and multiple component semiconductor metal oxides (e.g., ZnO-TiO₂, Bi₂O₃-ZnO) are categorized as first-generation and second-generation photocatalysts, respectively. The photocatalysts dispersed on an inert solid substrate (e.g., Ag-Al₂O₃, ZnO-C) are classified as third-generation photocatalysts. Finally, we reviewed the challenges that affect the photocatalytic degradation of dyes.

Hydrothermal synthesis, characterization and photocatalytic activity of Mg doped MoS2

In this research work nanoparticles of Mg (0, 1, 2 and 3%) doped MoS2 are prepared by Hydrothermal method at 200 °C for 9 h. Scanning Electron Microscope (SEM) for surface morphology, Fourier Transform Infrared Spectroscopy (FTIR) for structural and chemical bonding and UV-visible spectroscopy for optical properties are used. SEM showed that sheet-like structure has changed into stone-like shaped when Mg has doped into MoS2. From FTIR, Mo–O, Mo=S, and H–O bond peaks are becoming dim and new chemical bonds S=O, Mo=O, Mg–O, CH and OH are forming with the increase of Mg doping. UV-visible spectroscopy showed that MoS2 has an indirect bandgap 2.21 eV. Band gap decreased from 1.84 to 1.82 eV when the Mg doping was increased from 1 to 2%, respectively. As Mg concentration was increased i.e. 3% then band gap increased to 1.88 eV. Photocatalytic activity (PCA) of undoped and Mg doped MoS2 is appraised by degrading rhodamine blue (RhB) and methylene blue (MB) dyes. The results showed that PCA (in presence of visible light) Mg doped MoS2 is greater than pure MoS2 which significantly increased the photocatalytic properties.

Fabrication and characterization of Fe2O3, Bi2O3 and BiFeO3 and evaluation of their photo catalytic performances on degradation of methylene blue dye

This study reports the fabrication of Fe2O3, Bi2O3, and BiFeO3, characterization and evaluation of the photocatalytic performances for methylene blue dye degradation. The materials were synthesized by precipitation method and characterized by scanning electron microscopy, X-ray diffraction, energy dispersive X-rays analyses, and Fourier transform infrared analyses. The photocatalytic activities of Fe2O3, Bi2O3, and BiFeO3 were compared by performing degradation experiments with 50 mL of 100 mg/L methylene blue solution. The as-prepared BiFeO3 was found as 2.4 times and 1.7 times more effective than Fe2O3 and Bi2O3, with a 79, 47, and 57% catalytic activity, respectively. The degradation of methylene blue over the BiFeO3 catalyst was optimized in terms of pH, catalyst dosage, temperature, and methylene blue concentration. The Eley–Rideal mechanism was proposed to describe the reaction kinetics in terms of the first order and second order kinetics model. Activation energy E (kJ/mol), enthalpy ΔH (kJ/mol), entropy ΔS (J/mol) and free energy ΔG (kJ/mol) were calculated as 20.8, 18.2, 197.5 and −45.3 respectively. The negative value of free energy shows that photodegradation is favored in present conditions.

Kinetics and Equilibrium of Radioactive Metal Adsorption onto Sugarcane Bagasse Waste: Comparison of Batch and Column Adsorption Modes

Sugarcane bagasse waste biomass (SBWB) efficacy for the adsorption of Zr(IV) was investigated in batch and column modes. The process variables i.e. pH 1–4 (A), adsorbent dosage 0.0–0.3 g (B), and Zr(IV) ions initial concentration 25–200 mg/L (C) were studied. The experiments were run under central composite design (CCD) and data was analysed by response surface methodology (RSM) methodology. The factor A, B, C, AB interaction and square factor A2, C2 affected the Zr(IV) ions adsorption onto SBWB. The quadratic model fitted well to the adsorption data with high R2 values. The effect of bed height, flow rate and Zr(IV) ions initial concentration was also studied for column mode adsorption and efficiency was evaluated by breakthrough curves as well as Bed Depth Service and Thomas models. Bed height and Zr(IV) ions initial concentration enhanced the adsorption of capacity of Zr(IV) ions, whereas flow rate reduced the column efficiency.

Hydrothermal route for the synthesis of manganese ferrite nanoparticles and photocatalytic activity evaluation for the degradation of methylene blue dye

Manganese ferrite (MnFe2O4) was prepared via hydrothermal route and characterized by advanced techniques. The photocatalytic activity (PCA) was evaluated by degrading methylene blue (MB) dye under UV irradiation. The effect of process variables such as catalyst dose, UV exposure time and pH was studied for maximum degradation of dye at optimum conditions. The MnFe2O4 showed face centered cubic structure and average particle size of 23.98 nm. The lattice constant, lattice strain, ionic radii (rA & rB), bonding angles and hoping lengths of MnFe2O4 were recorded to be 0.8467 nm, 0.08, 1.66, 0.766, 1.833 and 2.116 Å, respectively. The MnFe2O4 showed promising PCA and at optimum conditions of process variable, up to 99% MB dye degradation was achieved. The PCA was found dependent to catalyst dose, UV exposure time and pH. Results revealed that the hydrothermal rout is feasible route for the preparation of MnFe2O4 ferrite in nano size and the PCA revealed the potential application of MnFe2O4 ferrite to degrade dye in textile wastewater.

Synthesis and Characterization of Co-ZnO and Evaluation of Its Photocatalytic Activity for Photodegradation of Methyl Orange

Photocatalysis is one of the techniques used for the eradication of organic pollutants from wastewater. In this study, Co-ZnO was tested as a photocatalyst for the degradation of methyl orange under irradiation of visible light. Co-ZnO loaded with 5%, 10%, and 15% Co was prepared by the precipitation method. The advanced techniques including X-ray diffraction, X-ray photoelectron spectroscopy, diffuse reflectance UV-visible spectroscopy, photoelectrochemical measurements, temperature-programmed desorption, photoluminescence, and fluorescence spectroscopy related to OH^• measurements were used for characterization of prepared Co-ZnO. Experiments showed that 10% Co-ZnO was a highly efficient catalyst for the photodegradation of methyl orange as compared to ZnO. The enhanced photocatalytic activity of Co-ZnO is attributed to the implantation of Co which inhibits the electron-hole recombination. A 100 mg/L solution of methyl orange dye was completely degraded within 130 min. The reaction kinetics has been described in terms of the Eley-Rideal mechanism.

ZnO, CuO and Fe2O3 green synthesis for the adsorptive removal of direct golden yellow dye adsorption: kinetics, equilibrium and thermodynamics studies

In the present investigation, ZnO, CuO and Fe2O3 were prepared via green route and utilized for the sequestration of DGY (Direct Golden Yellow) dye. Affecting variables i.e., temperature, contact time, adsorbent dose and pH were optimized for maximum sequestration of dye from aqueous medium. The pH 2, adsorbent dose 0.1 g/50 mL dye solution, temperature 30 °C and 50 mg/L dye initial concentration were best levels for efficient dye adsorption and equilibrium was attained in 30 min reaction time. The dye sequestration on to ZnO, CuO and Fe2O3 was an exothermic process. Freundlich and Temkin adsorption isotherms explained well the dye adsorption onto nanoadsorbents and dye adsorption followed pseudo first order kinetic model. Effect of electrolytes and heavy metal ions was also investigated and both affected the adsorption process significantly. In the presences of surfactant/detergent, the removal of dye was reduced and 0.5 N NaOH efficiently desorbed the dye from nanoadsorbents. Findings depicted that the nanoadsorbents are effectual for the sequestration of DGY dye, which can be employed for the remediation of textile effluents.

Dependence of the electrical properties of Cu-doped ZnO nanoparticles decorated by Ag atoms

Silver decorated copper doped zinc oxide nanoparticles (Ag@Cu-ZnO) were successfully prepared via sol gel method. X-ray diffraction analysis revealed ZnO wurtzite crystalline structure with the existence of minor peaks attributed to Cu and Ag. The presence of Cu and Ag in addition to ZnO lattice was supplementary verified by EDS data while the shift in the FTIR band confirmed the Cu incorporation within the ZnO host lattice. Both SEM and XRD revealed an increase in particle size with Ag loading. At different frequencies, electrical measurements demonstrated a decrement in the dielectric constant, dielectric loss and AC conductivity with the increment of Ag content. Meanwhile, the Nyquist plots of the impedance measurement showed a single semicircle arc indicating the predominance of grain boundary resistance. This study elucidated the great influence of Ag on Cu-doped ZnO nanoparticles’ structural, dielectric constant and electrical conductivity which make it a promising candidate for catalytic, photocatalytic and adsorption applications.

Dependence of the electrical properties of Cu-doped ZnO nanoparticles decorated by Ag atoms

Silver decorated copper doped zinc oxide nanoparticles (Ag@Cu-ZnO) were successfully prepared via sol gel method. X-ray diffraction analysis revealed ZnO wurtzite crystalline structure with the existence of minor peaks attributed to Cu and Ag. The presence of Cu and Ag in addition to ZnO lattice was supplementary verified by EDS data while the shift in the FTIR band confirmed the Cu incorporation within the ZnO host lattice. Both SEM and XRD revealed an increase in particle size with Ag loading. At different frequencies, electrical measurements demonstrated a decrement in the dielectric constant, dielectric loss and AC conductivity with the increment of Ag content. Meanwhile, the Nyquist plots of the impedance measurement showed a single semicircle arc indicating the predominance of grain boundary resistance. This study elucidated the great influence of Ag on Cu-doped ZnO nanoparticles’ structural, dielectric constant and electrical conductivity which make it a promising candidate for catalytic, photocatalytic and adsorption applications.

The Kinetics and Equilibrium Thermodynamics Study on the Removal of Direct Blue and Titan Yellow Dyes from Aqueous Media by Modified Rice Husk Char

The use of indigenous natural materials and their modification toward fruitful application is one of the important subjects. Thermal modification of Rice Husk at 400 oC resulted into Rice Husk Char (RHC) which was chemically modified with KOH and was labeled as KOH Modified Rice Husk Char (KMRHC). Both RHC and KMRHC were characterized by using, Fourier transformed infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-rays (EDX) and X-ray diffraction (XRD) before and after their use as adsorbents. The prepared material was applied for the removal of toxic dyes, Direct Blue (DB) and Titan Yellow (TY) from aqueous media. The maximum adsorption capacity of DB and TY dyes on KMRHC were inspected as 30.9 mg/g and 28.6 mg/g, respectively at pH 4 using initial dye concentrations of 80 mg/L containing 2500 mg/L of the adsorbent dose with agitation speed of 240 rpm at 303 K. At the same experimental conditions the highest percentage removal of DB and TY on the adsorbent were observed as 96.6% and 89.3%, respectively. Thermodynamics studies of the adsorption of DB and TY dyes on KMRHC inferred for exothermic and spontaneous process. The value of ΔS is negative which suggested that randomness decreases at the interface of adsorbent-adsorbate during the adsorption. The kinetics study indicated that the experimental data of the adsorption process for both dyes, best fits to pseudo-second order kinetic model. The equilibrium data was tested on Langmuir, Freundlich and Temkin adsorption isotherm models. It was observed that the data are best fit to the Langmuir isotherm model (R2 > 0.99), which suggested that the adsorption process is dominated by chemisorption approach. The overall results suggest that various parameters of the adsorption process were not only affected by the variation in experimental conditions but also by the chemical structure of the adsorbate molecules for the same adsorbent.

Microwave-Assisted Synthesis of Cobalt Oxide/Reduced Graphene Oxide (Co3O4–rGo) Composite and its Sulfite Enhanced Photocatalytic Degradation of Organic Dyes

One-pot synthesis of Co3O4 nanocrystals on reduced graphene oxide (rGO) was carried out by reacting cobalt nitrate, L-arginine, extract of Laportae aestuans as oxidant, fuel and reducing agent, respectively, in a domestic microwave. Morphologies of Co3O4–rGo (RGCO) composite was elucidated using UV-Vis, FT-IR, TEM, SEM, EDX, XRD and photoluminescence spectroscopies. The synthesized RGCO composite was applied as heterogeneous photocatalyst in the activation of Na2SO3 (sulfite) as sacrificial agent to degrade cationic dyes: rhodamine B (RhB) and methylene blue (MB), under visible light, at neutral pH 7.0. Photocatalytic performance of as-prepared RGCO was significantly enhanced in the presence of Na2SO3. Enhanced photocatalytic activity of RGCO was attributed to the synergistic effects between sulfite radicals generated in situ, and reduced graphene oxide, in which rGO served as electron sink to suppress recombination of photogenerated charge carriers. Plausible mechanistic pathways responsible for the activation of sulfite anions in situ are presented in this paper.

ZnO–TiO2: Synthesis, Characterization and Evaluation of Photo Catalytic Activity towards Degradation of Methyl Orange

Here in, we report the synthesis and characterization of ZnO–TiO2 composite as a potential photo catalyst for photo degradation of methyl orange under UV irradiation. ZnO–TiO2 with 1:1 ratio was synthesized via wet incipient impregnation method using TiO2 and Zn(NO3)2 ⋅ 6H2O as precursor material and the prepared composite was characterized by XRD, EDX and SEM. The synthesized composite was employed as photo catalyst for photo degradation of methyl orange. The photo degradation results showed that ZnO–TiO2 exhibited better catalytic performance than ZnO and TiO2 alone. The methyl orange photo degradation efficiency was determined to be 98, 75 and 60% over ZnO–TiO2, ZnO and TiO2 respectively using 50 mL solution of 100 mg/L at 40 °C for 120 min. The ZnO–TiO2 catalyzed photo degradation of methyl orange followed pseudo-first-order kinetic in terms of Langmuir–Hinshelwood mechanism.

Adsorption of 2,4-Dichlorophenoxyacetic Acid from Aqueous Solution Using Carbonized Chest Nut as Low Cost Adsorbent: Kinetic and Thermodynamic

The activated carbon was made of carbonized chest nut shell (CCS) and used as low cost adsorbent for 2,4-D (2,4-dichlorophenoxyacetic acid) removal. The experiments were conducted at different temperatures such as 35, 45 and 55 °C and this system represents as L type adsorption behavior. The experimental data were modelled using several isotherm models such as Langmuir, Freundlich, Temkin and Dubinin Radushkevich. The adsorption dynamics were searched by applying pseudo first, pseudo second and intra particle diffusion models. The thermodynamic approach was conducted for determining the thermodynamic values of ΔH°, ΔS° and ΔG°.

Metallurgical Processing Strategies for Metals Recovery from Industrial Slags

Slag produced as a byproduct in industrial processes, contains considerable metals contents, which need to be recovered to avoid environmental contamination. In present review, the types, applications, recovery of metals from slag and their hazardous effects have been discussed. Gravimetric, magnetic, floatation, pyrometallurgical and hydrometallurgical treatments are discussed for processing of charge chrome, steel, copper smelter, brass smelter, tin, incineration, ferrochrome and silico-manganese slags for the extraction of various metal ions (Mg, Cu, Zn, Pb, Cd, Ni, Co, Mn, Fe, As, Cr, Al, Nb, Ag, Au, Nb, Ta, Cu, Co, Ni, Fe, V, Cr). The possibility of biometallurgical processing of slags is also evaluated. Merits and demerits of extraction and purification techniques are highlighted with possible suggestions and possibility of integrated leaching techniques is also discussed.

Sol–Gel Synthesis of Mesoporous Silica–Iron Composite: Kinetics, Equilibrium and Thermodynamics Studies for the Adsorption of Turquoise-Blue X-GB Dye

Mesoporous silica (MPS) and MPS-Fe composite was prepared via sol–gel technique and characterized by BET, FTIR, XRD, SEM and pZc. The MPS and MPS-Fe adsorption efficiencies were evaluated for a cationic dye Turquoise-blue X-GB. The MPS-Fe composite showed pore size and BET values of 9.52 nm and 309 m2/g, respectively. XRD and SEM analysis revealed the amorphous nature and uniform distribution of spherical partciles with average particle size of 50 nm of MPS-Fe composite. The points of zero (pZc) charge found to be 2.3 and 6.3 for MPS and MPS-Fe, respectively. The MPS and MPS-Fe showed promising efficiency for the adsorption of Turquoise-blue X-GB as a function of medium pH, contact time, dye initial concentration and temperature. Among, Freundlich, Langmuir, Harkins–Jura, Temkin, Doubinin–Radushkevich isotherms, the Turquoise-blue X-GB followed Langmuir isothermal model with adsorption capacities of 83.34 mg/g and 74.07 mg/g for MPS and MPS-Fe composite, respectively. Among kinetics models, pseudo second order kinetic model fitted to the dye adsorption with R2 values of 0.998 and 0.988 for MPS and MPS-Fe composite, respectively. The negative values of enthalpy (ΔH) and free energy (ΔG) revealed exothermic and spontaneous adsorption of dye at room temperature. Results revealed that MPS and MPS-Fe composite have promising potential for Turquoise-blue X-GB dye adsorption and could possibly be extended for the adsorption of dyes from textile effluents.

Effect of Hydrothermal Reaction Time on Electrical, Structural and Magnetic Properties of Cobalt Ferrite

Cobalt ferrite was synthesized by hydrothermal route in order to investigate the effect of hydrothermal reaction time on structural, magnetic and dielectric properties. The synthesized cobalt ferrite was characterized by X-ray diffraction, Fourier transform infrared and Vibrating-Sample Magnetometer (VMS). XRD data analysis confirmed the formation of cubic inverse spinel ferrite for complete time series as the high intensity peak corresponds to cubic normal spinel structure. The ionic radii, cation distribution among tetrahedral and octahedral sites, lattice parameters, X-ray density, bond lengths were also investigated cobalt ferrite prepared at different hydrothermal reaction time. The crystallite size was found to be in the range of 11.79–32.78 nm. Tolerance factor was near unity that also confirms the formation of cubic ferrites. VSM studies revealed the magnetic nature of cobalt ferrite. The coercivity (1076.3Oe) was observed for a sample treated for 11 h. The squareness ratio was 0.56 that is close to 0.5 which shows uniaxial anisotropy in cobalt ferrite. Frequency dependent dielectric properties i.e. dielectric constant, AC conductivity, tangent loss and AC resistivity are calculated with the help of Impedance Analyzer. Intrinsic cation vibration of cubic spinel ferrites are confirmed from FTIR analysis in the range of 400–4000 cm−1. In view of enhanced properties, this technique could possibly be used for the synthesis of cobalt ferrite for different applications.

Adsorption of Dye from Wastewater onto ZnO Nanoparticles-Loaded Zeolite: Kinetic, Thermodynamic and Isotherm Studies

The adsorption process of methylene blue (MB) and its removal from aqueous solution at initial pollutant concentration range of 1–7 ppm was investigated. Zeolite-A (Z) and its ZnO-loaded species (Z/ZnO) were prepared via microwave technique from natural resource and applied for dye removal. The loading of ZnO was governed by the cation exchange property of zeolite, followed by calcination. Experimentally, Z and Z/ZnO were tested using X-ray Diffraction (XRD), Fourier-Transform Infrared (FTIR), Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDX) and N2 adsorption-desorption. The examined parameters such as concentration of dye, contact time, ZnO dose and solution pH were traversed. Three isothermal models were analyzed. Kinetic studies indicated that, the adsorption of MB matched with pseudo-second order model. The maximum removal efficiency at pH 3, increased from 67.8% for Z to 94.8% for Z/ZnO modified with 3% ZnO loads (Z/ZnO(3%)). Parameters such as ΔH, ΔS, ΔG, S* and Ea were thermodynamically calculated. Langmiur isotherm and pseudo-second order models were the best fitting for the obtained data. The results indicated that, the adsorption of MB dye is spontaneous and endothermic, the removal efficiency is favored by increasing the temperature. ZnO-zeolite has much higher adsorption capacity for eliminating MB dye than that of the un-loaded zeolite.

ZnO/UV/H2O2 Based Advanced Oxidation of Disperse Red Dye

In view of promising efficiency of advanced oxidation process, ZnO/UV/H2O2 based advanced oxidation process (AOP) was employed for the degradation of Disperse Red-60 (DR-60) in aqueous medium. The process variables such as concentration of catalysts, reaction time, pH, dye initial concentration and H2O2 dose were evaluated for maximum degradation of dye. The maximum degradation of 97% was achieved at optimum conditions of H2O2 (0.9 mL/L), ZnO (0.6 g/L) at pH 9.0 in 60 min irradiation time. The analysis of treated dye solution revealed the complete degradation under the effect of ZnO/UV/H2O2 treatment. The water quality parameters were also studied of treated and un-treated dye solution and up to 79% COD and 60% BOD reductions were achieved when dye was treated with at optimum conditions. The dissolved oxygen increased up to 85.6% after UV/H2O2/ZnO treatment. The toxicity was also monitored using hemolytic and Ames tests and results revealed that toxicity (cytotoxicity and mutagenicity) was also reduced significantly. In view of promising efficiency of UV/H2O2/ZnO system, it could possibly be used for the treatment of wastewater containing toxic dyes.

Green Synthesis of Metal Nanoparticles and their Applications in Different Fields: A Review

Nanotechnology is an art for application and handling of materials at very small scales i.e. 1–100 nm. The materials at this scale exhibit significantly different properties compared to same materials at larger scales. There are so many physical and chemical methods for the synthesis of nanoscale materials but the most appropriate are the ones that synthesize materials using green chemistry eco-friendly techniques. Recently, the collaboration between nanotechnology and biology has opened up new horizons of nanobiotechnology that integrates the use of biological materials in a number of biochemical and biophysical processes. This approach has significantly boosted up nanoparticles (NPs) production without employing harsh and toxic conditions and chemicals. This review is aimed to provide an outline of latest developments in synthesis of NPs through biotic entities and their potential applications.

A Novel Approach for Modification of Biosorbent by Silane Functionalization and its Industrial Application for Single and Multi-Component Solute System

The potential of an economically cheap raw material (rice husk) was evaluated in the present study to remove dyes including reactive yellow 15 (RY15) and reactive red 241 (RR241) in single and multi-component systems. The adsorbent was modified and functionalized chemically using glycidoxypropyltrimethoxysilane, sulfur and silane to enhance the removal efficiency of pollutants. The modified rice husk was evaluated by scanning electron microscope (SEM) and Fourier transform Infrared Spectroscopy (FTIR). Batch adsorption study showed that the modified rice husk with silane graft (RHSi) had highest removal efficiency of both dyes with 20% more removal compared to raw rice husk. The sorption correlated well with Langmuir, Freundlich, SIPS and Redlich-Peterson models for adsorption. Highest sorption was obtained at 10 mg L−1 of dye, 50 °C, 200 mg g−1 of adsorbent dose and pH 4. The mixture of two dyes poorly fit to the original Langmuir but fit best to the Langmuir-like model. This indicates that competitive Langmuir-like model considers that the capacities of adsorbents are equal. Results showed that the components compete for the available binding sites on adsorbent surface. It was also indicated that silane grafting can offer comparatively more binding sites compared to the raw rice husk and single-solute isotherm parameters cannot used for multi-component solute system.

Structural, Dielectric and Magnetic Studies of Perovskite [Gd1−xMxCrO3 (M = La, Co, Bi)] Nanoparticles: Photocatalytic Degradation of Dyes

Nanoparticles (NPs) of Gd1−xMxCrO3 (M = La, Co, Bi) were synthesized by microemulsion techniques, involving simultaneous single ion substitution philosophy. Structural, magnetic, dielectric properties, morphology, elemental analysis and distribution size of fabricated nano-crystalline were determined. The techniques employed for investigation are X-ray diffraction (XRD), vibrating sample magnetometer (VSM), dielectric measurement and scanning electron microscopy (SEM), energy dispersive X-ray (EDX), photoluminescence (PL) and atomic force microscopy (AFM), respectively. XRD pattern confirm that all the as-synthesized NPs have orthorhombic structure and successfully substituted of different metal ions into the regular crystal structure of GdCrO3. The lattice parameters X-ray density, bulk density, porosity and grain size were calculated from XRD pattern of Gd1−xMxCrO3 (M = La, Co, Bi) substituted and un-substituted GdCrO3. The magnetic hysteresis loop of fabricated product confirmed that the entire sample exhibits ferromagnetic behavior at room temperature. It was also found that the fabricated NPs show excellent photocatalytic activity (PCA) against Congo-red, about 78.24% after 55 min of incubation.

Hydrothermal Synthesis of Zinc Doped Nickel Ferrites: Evaluation of Structural, Magnetic and Dielectric Properties

Nickel–zinc ferrites are soft magnetic materials that have different technological applications due to their low magnetic coercivity, high electrical resistivity and low eddy current loss. The soft ferrites are the best for manufacturing core of power transformers, recording heads, data storage devices, telecommunication equipment, media devices, microwaves and electronic devices. In current investigation, a series of zinc doped nickel ferrites (ZnxNi1−xFe2O4, x = 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by hydrothermal method (at 220 °C, 16 h). The structural, magnetic and dielectric properties were measured. X-ray diffractometer and fourier transform infrared spectroscopy (FTIR) were used to analyze the structural properties and structure of zinc doped nickel ferrites was spinel. As the concentration of Zn was increased, the structural properties (lattice constant, density, dislocation density, radii of tetra and octahedral sites and oxygen positional parameters) were also changed. FTIR results showed the strongest absorption band at 500–600 cm−1, which indicate the intrinsic stretching vibration of Zn+2 ↔ O bond (Mtetra ↔ O) at tetrahedral site. Vibrating sample magnetometer (VSM) was used to measure magnetic properties and it was observed that the value of saturation magnetization increased with Zn concentration. The investigation of frequency dependent dielectric property was measured by Impedance Analyzer. Dielectric constant and tangent loss decreased at higher frequency, whereas AC conductivity increased with frequency.

Lead Remediation Using Smart Materials. A Review

The nanoparticles have been prepared and employed as excellent adsorbents for the sequestration of heavy metal ions and hazardous impurities from the aqueous media. The surface morphological, textural and structural properties of nanoparticles have been modified, which are capable and potentially useful for the remediation of metal ions. Several metals (oxides, doped, nanocomposites of Fe, Ti, Zn, SiO2, SiC, Mo, Co, Ni, Zr, Mn, Si, S, Al, Cu, Ce, graphene, CNTs) were reported an efficient adsorbents for the removal of lead (Pb) ions from aqueous media and polluted water. The present review focuses on different kinds of nanoparticles such as metal oxides, carbon based and host supported employed for removal of Pb ions under varying experimental conditions such as pH, temperature, contact time and concentrations. The preparation strategies, physicochemical properties and adsorption are also discussed. Based on studies, it was found that the smart materials are affective adsorbents for the purification of wastewater containing Pb ions and could possibly extended for the remediation of other heavy metal ions.

Structural and Optical Properties of Multilayer Heterostructure of CdTe/CdSe Thin Films

CdTe/CdSe multilayer heterostructures thin films were prepared by thermal evaporation method. The CdTe/CdSe layers deposited on glass substrate and effects of annealing temperature on optical and structural properties of thin films were investigated. The XRD analysis revealed that CdTe and CdSe were in cubic (111) and hexagonal (100) forms. By increasing the annealing temperature, intensity of XRD peaks increased for multilayer heterostructures. Band alignment in heterostructures of CdTe/CdSe was of type II. Energy band gaps values for CdTe/CdSe multilayer heterostructures increased with respect to bulk compounds. During emission, red and blue shifts are observed in visible region in photoluminescence spectrum of CdTe/CdSe samples. Due to better crystallinity of multilayer thin film, 1LO, 2LO and 3LO phonon modes were observed in Raman spectrum.

Synthesis and Characterization of ZnO Nanorods as an Adsorbent for Cr(VI) Sequestration

Zinc oxide (ZnO) nanorods were fabricated through hydrothermal route and employed for the adsorption of Cr(VI) ions from aqueous medium. Zinc nitrate hexahydrate (Zn(NO3)2.6H2O) was used as a zinc precursor and Triton-x 100 was used as a capping agent. As synthesized ZnO nanorods were characterized by UV-visible spectroscopy (UV), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-Ray spectroscopy (EDX) techniques. The adsorption affecting parameters were investigated for maximum adsorption of Cr(VI) onto ZnO nanorods. The adsorption kinetics, isotherms, and thermodynamics were applied for adsorption mechanism evaluation. Maximum adsorption of Cr(VI) ions (250 mg/g) was achieved using 0.055 g/L ZnO dose at pH 2.0 for the contact time of 30 min. Pseudo-second-order kinetic model and Langmuir isotherm explained well the Cr(VI) adsorption onto ZnO nanorods. The Cr(VI) adsorption onto ZnO was spontaneous and endothermic in nature. In view of promising adsorption efficiency, ZnO nanorods could possibly be used for Cr(VI) ions removal from wastewater and also extendable for the adsorption of other heavy metals ions.

Chemically Synthesized Hierarchical Flower like ZnO Microstructures

In the present study, we have deposited hierarchical flower-like microstructured zinc oxide (ZnO) thin films directly on a glass substrate by using the simplistic aqueous chemical route for different concentrations of triethanolamine (TEA) which acted like a complexing agent. The as-synthesized ZnO thin films were subsequently annealed at 300 °C and are characterized with characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), and electrical resistivity. The hexagonal wurtzite crystal structure of as-synthesized ZnO thin films was confirmed by their XRD patterns and the well-resolved ZnO flowers-like morphology was revealed from the FESEM micrographs. From FESEM images it can be seen that the ZnO flower is composed of dozens of nanorods originating from the same core in a symmetric fashion with an average diameter of around 180-300 nm. The flower-like morphology was obtained at 0.3 M TEA concentration. Due to its hierarchical structure, the deposited ZnO thin films were employed for multiple applications such as gas sensing and anti-microbial activity. The ZnO thin films with micro-flowers like morphology showed the maximum gas sensor sensitivity ∼64.50 at 150 °C for 100 ppm of NO2 gas. Moreover, the bacteria were completely destroyed in the presence of as-deposited ZnO thin films.

Identify the Active Phase of Fe–CN Composites for Oxidation Removal of Rhodamine B with H2O2

Fe-containing carbon nitrides (Fe–CN) prepared with various CN precursors, including dicyandiamide, melamine, guanidine hydrochloride and urea, were characterized by X-ray diffraction, thermal gravimetric analysis, N2 physisorption, transmission electron microscopy, X-ray photoelectron spectroscopy and atomic emission spectrometer measurements, and used as catalysts to catalyze the rhodamine B oxidation with H2O2 as oxidant. Characteristic results showed that Fe–CN exhibits different compositions, properties and catalytic performances if different CN precursors are used. The Fe–CN prepared from dicyandiamide contains mainly CN phase and certain amounts of surface Fe2O3 phase, exhibits the best activity; while that prepared from urea contains mainly Fe2O3 phase and few amounts of CN phase, exhibits the worst activity. Contrasting experiments conducted under light irradiation, with a supported Fe/CN_D catalyst, and that using a washed catalyst, suggested that the surface Fe2O3 is the active site of the reaction.

Photocatalytic Activity of Bismuth Ferrite Nanoparticles Synthesized via Sol-Gel Route

Nanosized, magnetically separable bismuth ferrite (BFO) nanoparticles, pertaining a crystallite size in the range of 14–15 nm were prepared via facile sol-gel technique. The product was characterized by scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The product was explored for the photocatalytic mineralization of rhodamine B (RB) dye in aqueous medium. The effect of different investigational parameters such as amount of photocatalyst, initial dye concentration and irradiation time on the photocatalytic degradation of RB was studied. The results reveal that the catalyst shows good degrading ability under normal pH and visible light conditions. BFO nanoparticles demonstrated a strong absorption ability in the visible-light region, which lead to efficient photocatalytic degradation of RB dye The reaction system was heterogeneous in nature in which the catalyst can be separated by a normal magnet.

Decolorization of Basic Turquise Blue X-GB and Basic Blue X-GRRL by the Fenton’s Process and its Kinetics

Textile industries use dyes to color their products and release waste water containing dyes, causing water pollution which is a serious problem for survival of human life on earth. The decolorization of basic turquise blue X-GB (BTB X-GB) 250% and basic blue X-GRRL (BB X GRRL) 250% dyes was examined by advanced (Fenton process) oxidation process. The effects of different parameters (initial dye concentration, pH, concentrations of hydrogen peroxide (H2O2) and reaction time) have been examined and optimum conditions were determined. It has been noted that percentage decolorization of both dyes (50 mg/L) increases with increase in concentration of H2O2. At optimum conditions (pH=3.0, H2O2=4.8 mM, temperature=50°C, time=80 min of BTB X-GB, and pH=5.0, H2O2=5.6 mM, temperature=40°C, time=60 min of BB X-GRRL) the decolorization obtained by Fenton process was 85.83% of BTB X-GB and 74.98% for BB X-GRRL. 1st order, 2nd order and BMG kinetic models were used to analyze the data. BMG model gives us the higher values of correlation coefficients for all data. Results showed that Fe2+/H2O2 are most effective for oxidation treatment of waste water effluents containing dyes as main pollutants.

The Differential Spectroscopic Investigation of Partitioning of Reactive Dyes in Micellar Media of Cationic Surfactant, Cetyl Trimethylammonium Bromide (CTAB)

This manuscript reports the solubilization of two reactive dyes viz. reactive black-5 (RB-5) and reactive black-8 (RB-8) in the micellar media of cationic surfactant, cetyl trimethylammonium bromide (CTAB) by differential UV/visible spectroscopy. Absorption spectra of said dyes in the presence of CTAB provide strong evidence about dye–surfactant interaction. In premicellar region ion association pair is formed between dye and surfactant while in post micellar region dye molecules get accommodated within the micelles. The values of critical micelle concentration (CMC) of CTAB in the presence of dyes, partition coefficient; Kx , free energy of partition, ∆Gp , binding constant, Kb and free energy of binding, ∆Gb were determined and compared for both dyes. It is, thus, concluded that RB-5 is solubilized to greater extent than RB-8 because of its incorporation in palisade layer of micelle close to micelle-water interface.

Optimal co-catalytic effect of NiFe2O4/ZnO nanocomposites toward enhanced photodegradation for dye MB

A series of magnetically recyclable NiFe2O4/ZnO nanocomposites have been successfully fabricated by a facile two-step route. The as-prepared NiFe2O4/ZnO nanocomposites were characterized by X-ray diffraction, field-emission scanning electron microscopy, vibrating sample magnetometer, ultraviolet-visible diffuse reflectance spectroscopy and photoluminescence spectroscopy. The results demonstrate that the NiFe2O4/ZnO nanocomposites are composed of ZnO particles (50–120 nm) integrated with NiFe2O4 particles (30–80 nm). Compared with bare ZnO, the NiFe2O4/ZnO nanocomposites exhibit evidently enhanced visible light absorption and decreased recombination of photo-generated electron-hole pairs. Moreover, the nanocomposites exhibit enhanced photocatalytic performance for the degradation of methylene blue under simulated solar light irradiation when compared with bare ZnO, and the 20%-NiFe2O4/ZnO nanocomposite is observed as the optimal composite. This is ascribed to the more efficient separation of photo-generated electron-hole pairs and generation of hydroxyl (˙OH) radicals in the 20%-NiFe2O4/ZnO nanocomposite. Furthermore, the NiFe2O4/ZnO nanocomposites have a high saturation magnetization, indicating that they can be magnetically separated and recycled from organic dye wastewater.

Preparation and Chemical Modification of Rice Husk Char for the Removal of a Toxic Dye (Orange G) from Aqueous Medium

The rice husk char (RHC) was prepared by keeping a known amount of the rice husk in furnace at 400°C. The product was modified with KOH and labeled as KOH modified rice husk char (KMRHC) which was used as an adsorbent for the removal of toxic dye, Orange G (OG) from aqueous media. Variation in the experimental conditions (agitation time, dye concentration, adsorbent dose, pH and temperature) play significant role in the adsorption process. The maximum adsorption capacity of OG on KMRHC was investigated as 38.8 mg/g at pH=4 using initial dye concentrations of 80 mg/L containing 2 g/L of the adsorbent dose with agitation speed of 250 rpm at 303 K. The % adsorption of dye was inspected as 96%. Thermodynamics studies of the adsorption of OG on KMRHC indicated that the value of ΔG and ΔH were negative which revealed that the adsorption process is exothermic and spontaneous process. The negative value of ΔS suggested that randomness decreases at the interface of adsorbent–adsorbate during the adsorption process. The kinetics study indicated that the experimental data of the adsorption process best fits to pseudo-second order kinetic model. The equilibrium data was tested on Langmuir, Freundlich and Temkin adsorption isotherm models. It was inspected that data follows all the three isotherm models (R2>0.91). However, the values of correlation coefficients (R2) indicated that the data is best fit to the Langmuir isotherm model (R2>0.99) which suggest for chemi-sorption process. The effect of temperature (303–343 K) shows that by varying the temperature the adsorption process is significantly affected. The general trend indicates that adsorption efficiency is higher at lower temperature as compared to higher temperature. This trend also suggests that the adsorption coefficient (K), rate of adsorption, and hence the spontaneity of adsorption process also decreases with raising the temperature.