This study utilized the magnetic Fe 3 O 4 ‐MnO 2 composite for As(III) removal by Box–Behnken design (BBD) model based on response surface methodology. The main objective of this study was to reduce the operational runs with the help of modeling with maximum accurate output and oxidized toxic from As(III) to As(V) with the help of MnO 2 , after that As(V) adsorbed on the composite surface. The composite had a good surface area (247.09 m 2 /g), magnetic property (16.50 emu/g), and mesoporous nature. Under batch‐optimized conditions, as obtained from the model (0.190 g composite dose, initial As(III) concentration 10.34 mg/L and pH 3.2) about 96% As(III) was removed from the aqueous solution. Langmuir model was able to describe the equilibrium data analysis with an uptake capacity of 81.16 mg/g. The adsorption process of As(III) on the Fe 3 O 4 ‐MnO 2 composite surface was best fitted to the pseudo‐second‐order kinetics model. Thermodynamics analysis suggested the spontaneous and endothermic nature of As(III) adsorption. The regenerated composite was able to remove 88% of As(III) and its stability was also checked up to the fourth cycle. Adsorption mechanism studies showed that As(III) oxidized to As(V) and then adsorbed on the Fe 3 O 4 ‐MnO 2 composite surface.

The impacts of various added substances on the morphology and related photocatalytic properties of different hematite (α-Fe2O3) nanostructures were examined. α-Fe2O3 croissant-like designs and finished microspheres were framed by aqueous treatment at 120 °C for 6 h within the sight of NaCl, Na2SO4, and Na2C2O4 as added substances, separately. After heat treatment in air, the photocatalytic movement of the α-Fe2O3 powder was surveyed by degrading methyl orange (MO) under UV light with hydrogen peroxide (H2O2) as an activator. The α-Fe2O3 progressive designs displayed the best photocatalytic activity with a 76.5% evacuation or degradation of dye molecules. This is credited to the high surface region of the iron oxide like morphology, which gives more dynamic locales for the degradation of dyes. The activation energy has also been well compared to the kinetic and isotherm models in the review, which shows that degradation of dyes on the outer layer of iron oxide is much more effective.

The unwanted industrial waste red mud (RM) embedded with Al(OH)3 was prepared and used for removal of Zn(II) ions from industrial wastewater. This prepared bio-adsorbent has brilliant efficiency towards zinc, which offers typical benefits including great adsorption capacity, easy preparation, and effective isolation from given aqueous solution. Several characterization techniques like FT-IR, XRD, SEM and EDX were employed for the adsorption process. From the results of kinetics and isotherm data, it has been inferred that the experiment was well-established to pseudo second order kinetics model with R2 value 0.9945 and followed Langmuir adsorption isotherm (R2=0.9938) with maximum adsorption capacity 26.87 mg/g at pH 5. The results suggested that the Al(OH)3/RM adsorbent material have strong affinity to zinc and could be used as an excellent adsorbent for treatment of zinc contaminated wastewater.

In the current scenario, removal of heavy metals from contaminated water has become a major challenging task to world researchers because disposal of untreated heavy metals into aquatic environment have adverse effect towards the ecosystem. Keeping this in mind, the present study investigates to synthesize the sugarcane bagasse biochar modified magnetic nanoparticles towards the decontamination and their batch scale potential of chromium (VI) from aqueous solution. The synthesized adsorbent was characterized by FT-IR, XRD, FE-SEM, VSM and EDX. The effect of adsorbent dosages (50-400 mg/L), initial Cr (VI) concentration (5-70 mg/L), pH (3-11), and contact time (1h-25h) were evaluated Cr (VI) removal on sugarcane bagasse biochar modified magnetic nanoparticles at room temperature. The adsorption data well fit with Langmuir isotherm (R2=0.99) and pseudo second order kinetics (R2=0.99). The maximum adsorption capacity was found to be 20.47 mg/g.

In this study, the waste neem leaves (Azadirachta indica) gained visible attraction for neem leaf–activated carbon (NLAC) preparation in the thermal process by using ammonium carbonate as an activating agent. Using NLAC, a nanocomposite of NLAC/Fe2O3 was synthesized by hydrothermal techniques for Cr(VI) elimination from the aqueous solution. The formation of NLAC/Fe2O3 composite was additionally confirmed by the use of various powerful investigative techniques such as FE-SEM, VSM, TEM, EDX, FT-IR, XRD, and BET. The NLAC/Fe2O3 has a saturation magnetization of 1.18 emu/g and surface area and pore volume of 245.2 m2/g and 0.038 cm3/g, respectively. The composite has crystalline structure and the average particle size of Fe2O3 present on the activated carbon surface was about 14–17 nm. The BBD (Box-Behnken design) model was used for Cr(VI) removal and the obtained R2 and adj-R2 values for the model were very high about 0.9805 and 0.9555. The ANOVA data indicated that the Cr(VI) model was a statistically significant one with the F and p values of 39.17 and 0.0001. About 91.4

This review investigated depth literature survey on the removal of various heavy metals and dyes contamination. The current study is a broad review of the different methods of preparation of biowaste adsorbent from rice husk and rice straw that has been implemented for the adsorption of many hazardous heavy metals and dyes in order to reduce their harmful effect on the environment. The selection of rice waste-based material for the adsorption process was considered due to its cost-effectiveness, easy availability, high adsorption efficiency, and reusability. This study is a comprehensive review of the adsorption of toxic heavy metals and dyes using rice husk and rice straw-based adsorbents either in bare or in modified forms under different physicochemical processes. In addition, some parameters affecting adsorption capability like pH, initial dye concentration, equilibrium time, temperature, adsorbent dosage, and shaking or stirring speed influence the adsorption mechanism have been discussed thoroughly. The applicability of various adsorption isotherm models and adsorption kinetic models for dye adsorption by various rice husk and straw biomass adsorbents is also reported here. Finally, from the literature reviewed conclusions have been drawn and also proposed a few future research suggestions.

Lead-free solid solution (1 − x) Na0.5Bi0.5TiO3–x BaTiO3, for x = 0.12 was successfully synthesized via sol–gel self-ignition wet chemical method. Choice of suitable dopants at proper sites (A and/or B) of a perovskite structure (ABO3 type) can modify the functional properties of the system. Here, we have systematically investigated the structural, micro-structural, vibrational, ferroelectric, dielectric phase transition and electrical properties of barium modified Na0.5Bi0.5TiO3 compound. Room temperature structural analysis (Rietveld and Raman spectroscopy) evident the formation of perovskite monophasic tetragonal phase. First-principles calculation based on density functional theory is in corroboration with the rietveld refined XRD results. The polydispersive nature of sample was confirmed from SEM imaging. The T-dependent dielectric spectra show diffused phase transition (Ferroelectric–Paraelectric) at a Curie temperature 255 °C. A well-defined real ferroelectric saturated hysteresis behaviour has been established upon E-poling the ceramics. From different types of conduction mechanism, bulk-limited space-charge conduction has been confirmed from J–E curve. Detailed electrical property studies on impedance spectroscopy and ac conductivity within the frequency range100 Hz–1 MHz have been investigated systematically on the polycrystalline sample in a broad thermal interval of 300–773 K. The assessed band gap value of ~ 3 eV in NBT-based ceramics recommend their use in power electronic devices.

Recently, nanoscale zero-valent iron (nZVI) particles have been efficiently used in the remediation of many heavy metals, yet potential agglomeration and loss of nZVI remain a critical area of research. In this study, we used red mud as a stable supporting medium to develop red mud modified nZVI to form (RM-nZVI) composite. We assessed its sorptive/reductive removal of mercury (Hg2+) from aqueous solutions. The RM-nZVI was synthesized through the reduction of ferric iron by sodium borohydride (NaBH4) in the presence of red mud. Morphological characterization of RM-nZVI confirmed its diffusion state with lesser aggregation. The RM-nZVI has the BET surface area, pore diameter, and pore volume as 111.59 m2g-1, 3.82 nm, and 0.49 cm3g-1, respectively. Adsorption of mercury (Hg2+) by RM-nZVI exhibits pH-dependent behavior with increased removal of Hg2+ with the increase in pH up to 5, and the removal rate decreased gradually as the pH increased from 5 to 10. Extensive characterization of RM-nZVI corroborated the evidence that the removal of Hg2+ was initially by rapid physical adsorption, followed by a reduction of Hg2+ to Hg0. The adsorption data were best fitted with Langmuir isotherm with R2 (correlation coefficient) > 0.99 with high uptake capacity of 94.58 (mg g-1). The novel RM-nZVI composite with enhanced sorptive and reductive capacity is an ideal alternative for removing Hg2+ from contaminated water.

In the present study, a magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite was synthesized by hydrothermal method and applied for As(III) removal by oxidation and adsorption process. Individual property of the entire material (i.e. magnetic property of Fe3O4, mesoporous surface property of C-dot and oxidation property of MnO2) make the composite efficient with good adsorption capacity for As(III) adsorption. The Fe3O4@C-dot@MnO2 nanocomposite had a saturation magnetization of 26.37 emu/g and it magnetically separated within 40 s. The Fe3O4@C-dot@MnO2 nanocomposite was able to reduce the 0.5 mg/L concentration of As(III) to 0.001 mg/L in just 150 min at pH 3. Pseudo-second-order kinetic and Langmuir isotherm model agreed with experimental data. The uptake capacity of Fe3O4@C-dot@MnO2 nanocomposite was 42.68 mg/g. The anions like chloride, sulphate and nitrate did not show any effect on removal but carbonate and phosphate influenced the As(III) removal rate. Regeneration was studied with NaOH and NaClO solution and the adsorbent was used for repeated five cycles above 80% removal capacity. The XPS studies proposed that As(III) first oxidized to As(V) then adsorb on the composite surface. This study shows the potential applicability of Fe3O4@C-dot@MnO2 nanocomposite to high extent and gives a suitable path for the proficient removal of As(III) from wastewater.

In this work, tea waste/CeO2 bio-composite was synthesized by using tea waste as the carbon matrix in a simple co-precipitation method and assessed for Cr(VI) remediation from contaminated water environment. The formed cerium oxide in bio-composite was crystalline, round in shape, 3-7 nm in size and the surface area of tea waste/ CeO2 bio-composite was 47.3 m(2)/g respectively. The bio-composite was able to remove 96% of Cr(VI) in the optimized condition of 0.8 g of adsorbent dose, pH 3, temperature 60 degrees C and initial concentration of 10 mg/L. Langmuir isotherm model and pseudo-second-order rate equation were fitted to the experimental conditions of this adsorption study. The bio-composite has an uptake capacity of 32.15 mg/g at pH 3. The material was effectively able to remove 85% of Cr(VI) in the fourth consecutive cycle. The FT-IR and Zeta potential analysis revealed that hydroxyl functional groups were responsible for Cr(VI) adsorption on the bio-composite surface. The principal mechanisms for this Cr(VI) removal study was mainly due to electrostatic attraction. Overall, the tea waste/CeO2 bio-composite can be a safe, promising, and novel adsorbent for real wastewater applications.

Chromium (Cr) contaminated water possesses a serious threat to the entire environment. Hence, approaches leading to the reduction of Cr concentration from aqueous media must be employed, primarily in industries so as to check the efflux of contaminants directly to water source. Recently chemical free synthesized nanoadsorbents have received much more attention essentially for the removal of different toxic metals from water. Therefore, in this work we have developed a plant-mediated synthetic route for the production of graphene oxide (GO) decorated MgO nanomaterial (GO-MgO) using Azadirachta indica (Neem) leaf extract and subsequently applied it as an efficient adsorbent for the removal of highly carcinogenic Cr(VI) ions from water. Different types of analytical techniques such as XRD, FTIR, Raman, BET, FESEM and HRTEM were used to estimate the formation, bonding, functionality, surface area and morphology of GO-MgO nanocomposite. The effect of adsorbent dose, pH of the solution, reaction time, concentration and co-existing ions were studied to estimate the Cr(VI) adsorption on GO-MgO surface. Maximum adsorption efficiency occurred at pH = 4 through electrostatic attraction between Cr(VI) species and GO-MgO surface with maximum uptake capacity value of 132.72 mg/g. The adsorption process followed Pseudo-second-order (PSO) kinetic and Langmuir isotherm models. The Cr(VI) adsorbed GO-MgO is recyclable and thus was reused up to five consecutive cycles.

A novel Lanthanum phosphate polyaniline (LaPO4-PANI) nanocomposite was synthesized by the simple sol-gel technique. The nanocomposite prepared at 1:1 ratio provided the highest ion exchange capacity and selective adsorption of Cr(VI). The phase composition and particle morphology of the as-prepared material was evaluated by XRD, FESEM and TEM analyses. The FTIR, Raman, and TGA data inferred the definite chemical interaction between the organic and inorganic counterparts in the formation of LaPO4-PANI. The selective adsorption of Cr(VI) was estimated by evaluating the distribution coefficient, electrical double layer theory as well as valency and Pauling's ionic radii of interfering ions (phosphate, iodide, sulfate, chloride, sulfide). The high tolerance capability of LaPO4-PANI against the interfering ions made it appropriate for selective and efficient removal of Cr(VI) ions from solutions. The nanocomposite showed the highest removal percentage of 98.6% towards Cr(VI) in a wide pH range of 2-6 at room temperature, as compared to sole lanthanum phosphate (56%) and polyaniline (75%). The XPS analysis revealed the adsorption mechanism due to the combined effect of both adsorption and reduction. Cr(VI) is adsorbed through electrostatic interactions while the = N-/-NH- group facilitated the in situ chemical reduction. The procured results make the LaPO4-PANI nanocomposite a promising adsorbent for the removal of Cr(VI). (C) 2021 Elsevier Ltd. All rights reserved.

Titania coated silica nanoparticles, which were synthesized via nanoparticle encapsulation route, are employed to degrade safranin-O dye from aqueous solution under UV light irradiation and were characterized by FT-IR, XRD, FESEM, N2 adsorption-desorption method and Zeta potential measurement. The results showed that the nanoparticles have a core-shell structure composed of about 100 nm of diameter of silica with several TiO2 fine particles in shell. After the degradation, this process is optimized through the response surface methodology (RSM). In this response study, photodegradation efficiency was evaluated by three main independent parameters such as catalyst dose, initial dye concentration and reaction time. Parameter sensitivity studies of the degradation efficiency of titania coated silica nanoparticles have shown 93.29% degraded under the optimal conditions of catalyst dose of 89.80 mg/g, initial dye concentration of 17.61 mg/L and reaction time of 12 min. We cross-checked the predicted values of degradation efficiency with the experimental values and were found to be in good agreement (R2=0.9983 and adj-R2=0.9967).

Red mud is a waste by product generated from alumina processing industries which creates a number of environmental problems. Reports of the utilization of the red mud for the treatment of natural, industrial and domestic waste water are available in literature. Clean water and a clean environment are the today’s requirements. The use of one waste for the removal of another waste is a challenging job. The present dissertation is an embodiment of the investigations for developing simple inexpensive adsorbents by the modification of red mud for waste water purification. In laboratory scale, neutralization of highly alkaline red mud is carried out by acid and CO2 gas treatment and modified by calcination. In another method, red mud adsorbent is prepared by surface modification with the impregnation of an anionic surfactant SDS. After modification, the red mud is called as Activated red mud (ARM) which is used as an adsorbent. The adsorbents (ARM) are used for the removal of Pb(II), Cd(II) ions and organic safranin-O dye separately from aqueous solutions in batch mode. The adsorbents, before and after treatment are characterized by XRD, SEM, EDX, TGA-DSC, FTIR, UV-Visible, BET surface area .The AAS analytical techniques is used to measure the residual metal ion concentration in treated water. The activated red mud used for the removal of hazardous Pb(II) possess the rounded shape aggregate particles with surface area 67.10 m2/g and particle size in the range of 0.1–150 µm . The maximum adsorption capacity as calculated from Langmuir isotherm model is found to be 6.0273 mg/g at pH 4. The pseudo-second-order kinetics describes the adsorption process. The adsorption process is described by ion exchange mechanism. The maximum adsorption capacities of Cd(II) on activated red mud (ARM) are found to be 12.046 and 12.548 mg/g at temperature 293 and 303 K, respectively. The endothermic, spontaneous and feasible nature of adsorption is known from the thermodynamic parameters. The external mass transfer coefficient (kf ) is found to be 0.084 ×10 -3, 0.012 ×10 -3 at temperature 293 K and 9.9 ×10 -3, 11.5 ×10 -3 at 303 K which are evaluated by the McKay et al: and Weber–Mathews equation respectively. The desorption efficiency of Cd(II) is found to be 91.29% with 0.2 mol/L HCl. The BET surface area of the SDS/RM is found to be 67.10 m2/g. The maximum adsorption capacity of modified red mud (SDS/RM) is found to be 8.94 mg/g at temperature 308 K and pH 4 obtained from Langmuir isotherm model. The external mass transfer coefficient (kf ) value as obtained from McKay et al: equation is found to be 3.49 ×10¬¬-4 , 4.61 ×10 -4 at temperature 308 K and 2.13 ×10 -4, 3.11 ×10 -4 at 328 K obtained from Weber–Mathews equation .These values indicate the faster adsorption of safranin-O on the surface of ARM at lower temperature. The response surface methodology (RSM) is applied to examine the efficiency of the removal of safranin-O dye from aqueous solution by the activated red mud neutralized by CO2 gas. A 24 full factorial central composite design (CCD) method is used to evaluate the effects of adsorption parameters. The operating parameters for maximum uptake capacity of 9.768 mg/g is; adsorbent dose (0.62 g), temperature (29.06 ℃), pH (8.3) and initial safranin-O concentration (37.3 mg/L). At this optimum condition, the adsorption of safranin-O from aqueous solution is found to be 94.5%.

Correction for ‘Removal of safranin-O dye from aqueous solution using modified red mud: kinetics and equilibrium studies’ by Manoj Kumar Sahu et al., RSC Adv., 2015, 5, 78491–78501.

Correction for ‘Adsorption of safranin-O dye on CO2 neutralized activated red mud waste: process modelling, analysis and optimization using statistical design’ by Manoj Kumar Sahu et al., RSC Adv., 2015, 5, 42294–42304.

Cobalt doped neutralized red mud (Co/NRM) nanocomposite materials were prepared by impregnation method for the photodegradation-of methylene blue dye under solar light irradiation. Different Co/NRM catalysts were prepared by varying the weight ratio of Co and NRM and characterized by different instrumental techniques. Under solar light 97.21% degradation was observed in the presence of 0.08 g of Co/NRM (Co:NRM::20:80) photocatalyst within 150 min for 20 mg/L methylene blue solution at pH 9. These results underline the potential use of effective, low-cost and easily available photocatalysts for the promotion of water splitting and environmental remediation under natural sunlight. (C) 2016 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Red mud is an undesirable by-product of bauxite in Bayer process has been used as a low-cost adsorbent for the removal of Cd(II) from aqueous solution by batch mode of experiment. The red mud was activated by acid dilution followed by ammonia precipitation for better adsorption of Cd(II). To achieve optimum condition for adsorption, different variable parameters were studied. X-ray diffraction, SEM and EDX were used to characterize the adsorbent before and after cadmium adsorption. The maximum adsorption capacities of Cd(II) on activated red mud (ARM) were found to be 12.046 and 12.548mgg(-1) at temperature 293 and 303K, respectively. Adsorption data of Cd(II) are best fitted to linearly transformed Langmuir isotherm with R-2>0.99. The pseudo-second-order model describes the kinetics of Cd(II) adsorption successfully to predict the rate constant of adsorption. Thermodynamic parameters reveal the endothermic, spontaneous and feasible nature of adsorption of Cd(II) onto ARM. The mass transfer study led to compute the external mass transfer coefficient (k(f)) by the equation of McKay et al. and Weber-Mathews at temperature 293 and 303K. The desorption efficiency of Cd(II) ions from ARM was 91.29% using 0.2-molL(-1) HCl.

The objective of the present research is to investigate the removal efficiency of As(V) from synthetic arsenic solution by Ce-Fe bimetal mixed oxide. The Ce-Fe bimetal mixed oxide is synthesized by solvothermal process and is characterized by using SEM, EDX, XRD, FTIR and BET. The analysis of SEM and BET analyser data of the material shows that particles are in the range of 290-300 nm, average pore size and surface area of the material is 4.42 nm and 127 m(2)/g respectively. Adsorption data are best fitted with the Langmuir isotherm with R-2 value of 0.9965. The maximum adsorption capacity is 32.12 mg/g at pH 3. Kinetics data revealed that the overall adsorption process followed pseudo-second-order kinetics. In the optimum conditions removal of As(V) using Ce-Fe bimetal mixed oxide is found to be 96%. The adsorption mechanism shows that the As(V) adsorption on the Ce-Fe bimetal mixed oxide is a complex mechanism including electrostatic attraction and the replacement of OH to form monodentate and bidentate complexes. The loaded adsorbent materials can be regenerated by using 0.5 M NaOH solution. (C) 2016 Elsevier Ltd. All rights reserved.