Removal of methylene blue by Polyaniline/TiO2 hydrate: Adsorption kinetic, isotherm and mechanism studies

Research upon Cu-Doping Contents in TiO2 Nanoparticles Incorporated onto Cellulose Nanofibers for Dye Removal and Self-Cleaning Applications

Cu-doping contents in the TiO2 lattice structure were studied to show the effects on the crystal structure, morphology, and photocatalytic activity of TiO2 nanoparticles and thus composite cellulosic nanofibrous membranes. Pristine and copper-doped TiO2 nanoparticles were synthesized using the sol-gel technique, a wet chemical method with the advantages of low synthesizing temperature, uniform nanosize distribution, and purity. The as-synthesized semiconductor nanoparticles were first tested with the dye removal process and then impregnated onto electrospun cellulose nanofibers (CL nanofibers) to acquire modified nanofibers with self-cleaning properties. The as-prepared composite CL nanofibers consisting of doped and undoped TiO2 nanoparticles were characterized by various techniques, such as field emission scanning electron microscopy, transmission electron microscopy, UV-vis, X-ray diffraction, Fourier transform infrared spectroscopy, and tensile tests. The copper-doped TiO2 molar ratio in the nanocomposite was found to possess a pronounced impact on the dye removal and self-cleaning effects under the visible light spectrum, whereas TiO2 is highly effective under specific UV-light irradiation. Optical measurements and dye decomposition showed that the Cu-doped TiO2 nanocomposite was optimized at a 1% molar ratio by the copper-doping concentration regarding dye removal and self-cleaning applications under the visible light range.

Synthesis and characterization of new composite from modified silica-coated MnFe2O4 nanoparticles for removal of tetracycline from aqueous solution

In this study, a new composite from silica coated MnFe2O4 nanoparticles, diethylenetriamine, 3-chloropropyl trimethoxysilane and Mg-Al Layered Double Hydroxide (Mg-Al LDH/DETA/CPTMS/SCNPs) composite was synthesized. The Mg-Al LDH/DETA/CPTMS/SCNPs composite was examined by Fourier transform infrared spectrometer (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDS), X-ray diffraction (XRD), Thermogravimetric Analysis (TGA) and Vibrating Sample Magnetometry (VSM). The synthesized composite exhibited magnetic property with a saturation magnetization of 0.40 emu g-1. The Mg-Al LDH/DETA/CPTMS/SCNPs composite was utilized as a successful adsorbent for removal of tetracycline from aqueous solutions. The effect of various operation factors such as initial drug concentration, adsorbent dosage, pH and contact time were investigated. The optimized variable conditions such as adsorbent dose of 60 mg L-1, drug concentration of 100 mg L-1, pH = 7 and contact time 30 min were obtained. For describing the adsorption isotherms, the Langmuir, Freundlich and Temkin adsorption models were utilized. The results indicated that the adsorption isotherm is in good agreement with Langmuir model. According to the Langmuir analysis, the maximum adsorption capacity (qm) of the Mg-Al LDH/DETA/CPTMS/SCNPs composite for tetracycline was obtained to be 40.16 mg g-1. The kinetic studies revealed that the adsorption in all cases to be a pseudo second-order process. The negative value of ΔG° and the positive value of ΔH° showed the adsorption process to be spontaneous and endothermic.

Explorative Image Analysis of Methylene Blue Interactions with Gelatin in Polypropylene Nonwoven Fabric Membranes: A Potential Future Tool for the Characterization of the Diffusion Process

This manuscript explores the interaction between methylene blue dye and gelatin within a membrane using spectroscopy and image analysis. Emphasis is placed on methylene blue's unique properties, specifically its ability to oscillate between two distinct resonance states, each with unique light absorption characteristics. Image analysis serves as a tool for examining dye diffusion and absorption. The results indicate a correlation between dye concentrations and membrane thickness. Thinner layers exhibit a consistent dye concentration, implying an even distribution of the dye during the diffusion process. However, thicker layers display varying concentrations at different edges, suggesting the establishment of a diffusion gradient. Moreover, the authors observe an increased concentration of gelatin at the peripheries rather than at the center, possibly due to the swelling of the dried sample and a potential water concentration gradient. The manuscript concludes by suggesting image analysis as a practical alternative to spectral analysis, particularly for detecting whether methylene blue has been adsorbed onto the macromolecular network. These findings significantly enhance the understanding of the complex interactions between methylene blue and gelatin in a membrane and lay a solid foundation for future research in this field.

Preparation of PANI modified TiO2 and characterization under pre- and post- photocatalytic conditions

Polyaniline (PANI) is a promising conducting polymer for surface modification of TiO2 to overcome limitations of the use of visible light and attain increased photocatalytic efficiency for the removal of organic contaminants. In this study, a series of polyaniline modified TiO2 (PANI-TiO2) composites were prepared by using "in-situ" chemical oxidation polymerization method. The composites were systematically characterized by Fourier transform infrared spectroscopy (equipped with an attenuated total reflection accessory, FTIR-ATR), Raman spectroscopy, X-ray diffractometry (XRD), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDAX), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL), nitrogen (N2) physisorption (Brunauer - Emmett - Teller surface area (SBET) and Barrett-Joyner-Halenda (BJH) pore size analysis), thermogravimetry-derivative thermogravimetry (TG-DTG) techniques. XRD patterns of PANI-TiO2 composites confirmed both the amorphous phase of PANI and the crystalline character of TiO2. TG/DTG analysis complemented the XRD profiles that the interactions between PANI and TiO2 resulted in a more stable PANI-TiO2 matrix. SEM images displayed the dominant morphology as dandelion-like shapes of PANI being more pronounced with increasing PANI ratios in PANI-TiO2 composites. UV-DRS profiles revealed that the band gap energies of the composites were lower than bare TiO2 expressing a shift to the visible light region. Both PL and UV-DRS analyses confirmed the band-gap reduction phenomenon of PANI modification of TiO2. The incorporation of PANI into TiO2 resulted in a reduction of the surface area of TiO2. The composites were subsequently subjected to photocatalytic activity assessment tests using humic acid (HA) as a model of refractory organic matter (RfOM) under simulated solar irradiation (Uyguner-Demirel et al. Environ Sci Pollut Res 30 85626-85638, 2023). The morphological and structural changes attained upon application of photocatalysis were also evaluated by FTIR-ATR, Raman spectroscopy, XRD, and SEM-EDAX methods in a comparable manner. The FTIR-ATR spectral features of PANI, RfOM and all composites displayed peaks with slight shifts under pre- and post- photocatalytic conditions as well as following dark surface interactions. Besides exhibiting noticeable photocatalytic performance, PANI-TiO2 composites were also proven to maintain stability under non-selective oxidation conditions in the presence of a complex organic matrix. The prepared PANI-TiO2 composites overcoming the limitations of UVA light active bare TiO2 photocatalysis could possibly find a beneficial use as potential catalysts in solar photocatalytic applications.

Nano-silica from white silica sand functionalized with PANI-SDS (SiO2/PANI-SDS) as an adsorbent for the elimination of methylene blue from aqueous media

Natural resources including sand are one of the best approaches for treating dye-polluted wastewater. The SiO2/PANI-SDS nanocomposite was synthesized by self-assembly and intermolecular interaction. The physicochemical features of the SiO2/PANI-SDS nanocomposite were explored by FT-IR, XRD, SEM, TEM, EDX, and N2 adsorption-desorption techniques to be evaluated as an adsorbent for the MB. The surface area of the SiO2/PANI-SDS is 23.317 m2/g, the pore size is 0.036 cm3/g, and the pore radius is 1.91 nm. Batch kinetic studies at different initial adsorbate, adsorbent and NaCl concentrations, and temperatures showed excellent pseudo-second-order. Several isotherm models were applied to evaluate the MB adsorption on the SiO2/PANI-SDS nanocomposite. According to R2 values the isotherm models were fitted in the following order: Langmuir > Dubinin-Radushkevich (D-R) > Freundlich. The adsorption/desorption process showed good reusability of the SiO2/PANI-SDS nanocomposite.

Adsorption mechanism of methylene blue by magnesium salt-modified lignite-based adsorbents

The rich pore structure and carbon structure of lignite make it a suitable adsorbent for effectively removing methylene blue (MB) from wastewater. This article reports the preparation of lignite-based adsorbents modified by magnesium salts, and the key factors and adsorption mechanism are analyzed to effectively improve the adsorption performance for MB. The results showed that the lignite was modified by magnesium salts, and the Mg2+ in the magnesium salts had a good binding effect on the oxygen-containing functional groups in the lignite. This improved the adsorption performance of the lignite-based adsorbents for MB. The Mg(NO3)2-modified lignite-based adsorbent showed the best adsorption performance and removal rate of MB (99.33%) when prepared with 8 wt % Mg(NO3)2. Characterization analysis showed that a "-COOMg" structure was formed between Mg2+ in the magnesium salts and the carboxylic acid functional group in the lignite, which was postulated to be the absorption site that promoted the adsorption performance for MB. It is speculated that the MB adsorption mechanism of this lignite-based adsorbent is ion exchange.

Synthesis of submicron ferrous oxalate from red mud with high Fenton catalytic performance on degradation of methylene blue

Ferrous oxalate dihydrate (FOD) can be used as a photo-Fenton catalyst with remarkable photo-Fenton catalytic and photocatalytic performances on organic pollutant degradation. Various reduction processes were compared in the current study to synthesize FODs from ferric oxalate solution utilizing the iron source in alumina waste red mud (RM), including natural light exposure (NL-FOD), UV light irradiation (UV-FOD), and hydroxylamine hydrochloride hydrothermal method (HA-FOD). The FODs were characterized and employed as photo-Fenton catalysts for methylene blue (MB) degradation, and the effects of HA-FOD dosage, H2O2 dosage, MB concentration, and the initial pH were investigated. The results show that HA-FOD has submicron sizes and lower impurity contents with more rapid degradation rates and higher degradation efficiencies compared with the other two FOD products. When using 0.1 g/L of each obtained FOD, 50 mg/L of MB can be rapidly degraded by HA-FOD by 97.64% within 10 min with 20 mg/L of H2O2 at pH of 5.0, while NL-FOD and UV-FOD achieve 95.52% in 30 min and 96.72% in 15 min at the same conditions, respectively. Meanwhile, HA-FOD exhibits strong cyclic stability after two recycling experiments. Scavenger experiments reveal that the predominant reactive oxygen species responsible for MB degradation are hydroxyl radicals. These findings demonstrate that submicron FOD catalyst can be synthesized using hydroxylamine hydrochloride hydrothermal process from ferric oxalate solution with high photo-Fenton degradation efficiency and reduced reaction time for wastewater treatment. The study also provides a new pathway of efficient utilization for RM.

Photocatalytic performance of PANI modified TiO2: Degradation of refractory organic matter

Surface modification of TiO2 with polyaniline (PANI) conducting polymer has been used to achieve visible light photoresponse, thereby increasing solar photocatalytic activity. In this study, photocatalytic performances of PANI-TiO2 composites with different mole ratios were synthesized by the in situ chemical oxidation polymerization method and tested for the degradation of a model refractory organic matter (RfOM), namely humic acid in an aqueous medium under simulated solar irradiation in a comparative manner. Adsorptive interactions under dark conditions and interactions under irradiation were investigated as contributing factors to photocatalysis. Degradation of RfOM was monitored in terms of UV-vis parameters (Color436, UV365, UV280, and UV254) and fluorescence spectroscopic parameters as well as the mineralization extent by dissolved organic carbon contents. The presence of PANI exerted an enhancement in photocatalytic degradation efficiency compared to pristine TiO2. The synergistic effect was more pronounced in lower PANI ratios whereas higher PANI ratios reflected a retardation effect. Degradation kinetics were assessed by pseudo-first-order kinetic model. For all UV-vis parameters analyzed, highest and lowest rate constants (k) were attained in the presence of PT-14 (2.093 × 10-2 to 2.750 × 10-2 min-1) and PT-81 (5.47 × 10-3 to 8.52 × 10-3 min-1), respectively. Variations in selected absorbance quotients, i.e., A254/A436, A280/A436, and A253/A203, were distinctive and compared with respect to irradiation time and photocatalyst type. Upon use of PT-14, a steady decreasing profile with respect to irradiation time was attained for A253/A203 quotient as 0.76-0.61, followed by a rapid decrease to 0.19 in 120 min. The incorporation effect of PANI into TiO2 composite could be visualized in A280/A365 and A254/A365 quotients exhibiting an almost constant and parallel trend. As a general trend, decrease in the major fluorophoric intensity FIsyn,470 with photocatalysis was observed under extended irradiation conditions; however, an abrupt decline was remarkable in the presence of PT-14 and PT-18. Fluorescence intensity decrease correlated well with spectroscopic evaluation of rate constants. A thorough evaluation of spectroscopic parameters of UV-vis and fluorescence can provide significant information for practical applications in control of RfOM in water treatment.

Functionalized MoO3 Nanosheets for High-Efficiency RhB Removal

2D nanostructured materials have been applied for water purification in the past decades due to their excellent separation and adsorption performance. However, the functional 2D nanostructured molybdenum trioxide (MoO3)has rarely been reported for the removal of dyes. Here, functionalized MoO3 (F-MoO3) nanosheets are successfully fabricated with a high specific surface area (106 cc g-1) by a one-step mechanochemical exfoliation method as a highly effective adsorbent for removing dyes from water. According to the Raman, X-ray photoelectron spectroscopy, Fourier transform infrared (FTIR), and selected area electron diffraction analysis, functional groups (hdroxyl groups, amide groups, amine groups and amino groups) are identified in the as-prepared F-MoO3 nanosheets. The attached functional groups not only facilitate the dispersal ability of F-MoO3 nanosheets but also enhance the adsorption capacities. Thus, the performance (up to 556 mg g-1 when the initial concentration of Rhodamine B solution is 100 mg L-1) of as-prepared F-MoO3 nanosheets is almost two times higher than other reported MoO3 materials. Furthermore, the FTIR spectra, isotherm, and several factors (e.g., adsorbent dosage and adsorbate dosage) are also systematically investigated to explore the adsorption mechanism. Therefore, this work demonstrates that the F-MoO3 nanosheets are a promising candidate for wastewater treatment.

Biopolymer templated strategized greener protocols for fabrication of ZnO nanostructures and their application in photocatalytic technology for phasing out priority pollutants

Zinc oxide (ZnO) nanostructures have been successfully synthesized via template-assisted and template-free route using three different synthetic methods, i.e., sonochemical, mechanochemical, and hydrothermal. Biopolymer xanthan gum (XG) served as sacrificial template for ZnO synthesis as provided the surface for the growth of nanostructures in a controlled manner. The employment of multifarious synthetic techniques resulted in fabrication of ZnO nanoparticles with diverse morphologies such as needle shaped, hexagonal, and spherical particles. Further, the template-assisted protocols generated thermally stable highly crystalline nanostructures along with high surface area, larger pore size, and low band gap energies in contrast to template-free protocol. The structural and other physicochemical studies were manifested by XRD, N₂ adsorption desorption, FESEM, TGA, and UV-Vis spectral analysis. The template-assisted ZnO nanostructures were explored as a potential photocatalyst for the catalytic degradation of emerging pollutants, i.e., triclosan (TCS) and imidacloprid (IMD) under the exposure of UV light. The products formed during the photocatalytic reaction were monitored by UV-Vis spectroscopy and HPLC. The results obtained revealed the high catalytic efficiency of ZnO synthesized via template-assisted sonochemical method for TCS (99.60%) and IMD (96.09%) which is attributed to the high surface area and lower band gap energy of the catalyst. The high catalytic potential of the sonochemically synthesized ZnO also substantiated from the kinetic data as high-rate constant was obtained. Thus, the template-assisted protocols developed led to preparation of nanostructures having tailored properties for efficient photocatalysis and can rapidly degrade selected emerging contaminants such as personal care products and organophosphate pesticides. Hence, environment-friendly synthesized photocatalyst can be appropriately employed to wastewater treatment contaminated with emerging pollutants.

Removal of methylene blue dye from aqueous solution using an efficient chitosan-pectin bio-adsorbent: kinetics and isotherm studies

Wastewater contains organic compounds, including dyes, which have potential risks to the environment. Hence, these compound needs to be eliminated from the aqueous solution. In the present study, chitosan-pectin composite (Cs-Pc) was used as an adsorbent to remove methylene blue dye (MB) from synthetic wastewater. To evaluate the parameters affecting adsorption, including the initial MB concentration, solution pH, contact time, and Cs-Pc dose, batch experiments were carried out. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR), and pH point of zero charges (pH pzc) were applied for characterizations of Cs-Pc. The optimum conditions were obtained with an initial MB concentration of 50 mg L^-1: solution pH ~ 11, Cs-Pc dose: 1.5 g L^-1 and 180 min contact time, which caused 97.77% of MB removal. In addition, the removal efficiency of MB was more influenced by pH than by sorbate dose. Also, Cs-Pc had a higher ability to remove MB than chitosan and pectin, probably due to its highly porous structure and rough surfaces that provides active sites and facilitate MB adsorption. The maximum removal efficiency and the adsorption capacity of MB onto Cs-Pc at 500 mg L^-1 concentration under optimum conditions were 98.67% and 328.02 mg g^-1, respectively. The adsorption kinetics and isotherms were best described by pseudo-second-order and Freundlich equation, respectively. After four times of recycling, the removal efficiency of MB was above 96%. Electrostatic and pi-pi interactions are the main mechanisms for the removal of MB onto the adsorbent. So the application of Cs-Pc is promising for MB removal from polluted solutions not only due to its strong adsorbing capability but also due to its excellent ability to reuse.

Polyaniline/Bi12TiO20 Hybrid System for Cefixime Removal by Combining Adsorption and Photocatalytic Degradation

Sillenite catalysts have shown efficient photocatalytic activity for the removal of various pollutants from water in previous studies, thus enhancing their activity by combining them with other materials will be very promising for environmental applications. In this context, an interesting hybrid system containing Polyaniline (PANI) as an adsorbent and Bi12TiO20 (BTO) sillenite as a catalyst was proposed in this work. Cefixime (CFX) has been selected as a pollutant for this study, and its removal was evaluated using PANI (adsorption), PANI and BTO (combined system) and the hybrid system Bi12TiO20/Polyaniline (BTO/PANI). First, the impact of PANI adsorption was investigated on its own; after that, the solution was filtered to separate the adsorbent from the liquid in order to re-treat the solution using photocatalysis (combining adsorption with photocatalysis). At the same time, a similar technique was used involving the hybrid system BTO/PANI. The results show that the hybrid system can remove a very high Cefixime concentration of 30 mg/L, almost 100%, within only 2 h, and this is better than previous investigations. These results indicate that it is possible to combine photocatalysis and adsorption processes to control water pollution.

Regulating Alkyl Chain Length on Quaternization TiO2 for Boosting Photocatalytic Performance: Synergism of Promoting Photogenerated Charge Separation and Improving Reactant Adsorption

To explore the effect of surface charge properties of a photocatalyst on photocatalytic activity, quaternization TiO₂ particles with different alkyl chain lengths (CT-X/P25) are first synthesized to boost the photocatalytic activity. The effect of a quaternary ammonium group with different alkyl chain lengths on the photocatalytic activity of CT-X/P25 is investigated. Interestingly, the introduction of a quaternary ammonium group on CT-X/P25 not only contributes to improving the photodegradation efficiency of anionic dyes due to enhancing of adsorption capacity through electrostatic attraction, but also it can improve the photodegradation efficiency of cationic dyes. Therefore, there seems to be another factor affecting the photocatalytic activity. The results of photoelectric characterization show that the photogenerated charge separation of CT-X/P25 is greatly enhanced, which is beneficial to improve the photocatalytic activity. Simultaneously, the results show that the difference in the photocatalytic activity of CT-X/P25 is mainly related to the charge intensity of -N⁺(CH₃)₂- in the quaternary amine salt. According to X-ray photoelectron spectroscopy, the charge intensity of -N⁺(CH₃)₂- in CT-X/P25 gradually increases with the increase in alkyl chain lengths, which is conducive to promoting photogenerated charge separation and improving the adsorption for anionic dyes. The photocatalytic activity has been further enhanced due to the enhancement of this synergy. In summary, the quaternary ammonium salt-modified CT-X/P25 shows an excellent synergistic effect on the process of photodegradation of anionic dyes: promoting photogenerated charge separation and adsorption.

Optimization of CO2 Sorption onto Spent Shale with Diethylenetriamine (DETA) and Ethylenediamine (EDA)

A novel technique was employed to optimize the CO₂ sorption performance of spent shale at elevated pressure-temperature (PT) conditions. Four samples of spent shale prepared from the pyrolysis of oil shale under an anoxic condition were further modified with diethylenetriamine (DETA) and ethylenediamine (EDA) through the impregnation technique to investigate the variations in their physicochemical characteristics and sorption performance. The textural and structural properties of the DETA- and EDA- modified samples revealed a decrease in the surface area from tens of m²/g to a unit of m²/g due to the amine group dispersing into the available pores, but the pore sizes drastically increased to macropores and led to the creation of micropores. The N-H and C-N bonds of amine noticed on the modified samples exhibit remarkable affinity for CO₂ sequestration and are confirmed to be thermally stable at higher temperatures by thermogravimetric (TG) analysis. Furthermore, the maximum sorption capacity of the spent shale increased by about 100% with the DETA modification, and the equilibrium isotherm analyses confirmed the sorption performance to support heterogenous sorption in conjunction with both monolayer and multilayer coverage since they agreed with the Sips, Toth, Langmuir, and Freundlich models. The sorption kinetics confirm that the sorption process is not limited to diffusion, and both physisorption and chemisorption have also occurred. Furthermore, the heat of enthalpy reveals an endothermic reaction observed between the CO₂ and amine-modified samples as a result of the chemical bond, which will require more energy to break down. This investigation reveals that optimization of spent shale with amine functional groups can enhance its sorption behavior and the amine-modified spent shale can be a promising sorbent for CO₂ sequestration from impure steams of the natural gas.

Unravelling the Methylene Blue Adsorption Mechanism on Doped and Nondoped Polyaniline: A Combined Molecular Modeling and Experimental Investigation

A multiscale investigation including computational chemistry calculations and experimental studies was performed to elucidate and understand the methylene blue (MB) adsorption on polyaniline (PANI) from an aqueous solution. Static DFT and DFT-based ab initio molecular dynamics were used to characterize the intermolecular interactions of this dye molecule with nondoped and doped PANI. Experimental adsorption studies at different operating conditions were performed to complement the mechanism analysis of this adsorption system. Infrared spectroscopy studies and ab initio calculations showed the important role of π-π stacking and van der Waals interactions for the dye adsorption on PANI. Experimental results of MB adsorption on the PANI surface indicated that alkaline conditions were more favorable than acidic conditions where the MB adsorption capacity ranged from 9.91 mg/g at pH 1.8 to 23.16 mg/g at pH 10.9. Equilibrium adsorption studies with nondoped PANI revealed a fast removal of the dye molecules where the equilibrium adsorption was reached after 45 minutes. The kinetic parameters were calculated with the pseudo-second and pseudo-first order models, while the adsorption mechanism was analyzed using the intraparticle diffusion, Boyd, and Elovich models. Dye adsorption equilibrium was studied at pH 8 and 30 °C where Temkin, Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) isotherm models as well as a statistical physics monolayer model were employed in data analysis. The saturation dye adsorption capacity was 40.2 mg/g where an inclined adsorption orientation of dye molecules on the PANI surface could be expected with an adsorption energy of 14.0 kJ/mol. This interaction energy clearly indicated that only physical interactions were involved in the MB dye adsorption mechanism, which was also confirmed by the calculations with the D-R isotherm model. These theoretical and experimental results are important to understand the dye adsorption properties of conductive polymers and to consolidate their application in the synthesis of new adsorbents and composites for water treatment.

A Study of Methylene Blue Dye Interaction and Adsorption by Monolayer Graphene Oxide

The graphene oxide (GO) interaction with methylene blue (MB) cationic dye was studied in an aqueous solution at different pH during MB adsorption. The mutual interaction of MB with GO surface was studied and evaluated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The π-π and electrostatic interaction of MB with GO surface are the main types of interactions, and the XRD data show the monomeric arrangement of MB cation with GO. The GO surface functional groups and point of zero charge (PZC) were determined by acid-base titration. Suitability of zeta-potential measurement and acid-base titration method was briefly discussed. The quality of prepared GO was evaluated by Raman spectroscopy, XRD, and atomic force microscope (AFM). The experimental adsorption equilibrium data were analyzed using Langmuir, Langmuir-Freundlich, Freundlich, and Temkin isotherms. The GO maximum adsorption capacity increases with higher pH, that is ascribed to the facile interaction of negatively charged GO with positively charged MB structure.

Synthesis, Characterization, and Application of Magnetized Lanthanum (III)-Based Metal-Organic Framework for the Organic Dye Removal from Water

A hybrid composite based on metal-organic framework (MOF) was chemically fabricated by embedding the magnetic Fe3O4 nanoparticles within amino-functionalized porous La-MOF (MOF/NH2) to produce a highly efficient and reusable composite of MOF/NH2/Fe3O4. Different proper techniques were used for the characterization of surface morphology and chemical arrangement of the prepared MOF/NH2/Fe3O4 composite. The characterization results using various techniques including Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer, Emmett, and Teller analysis (BET), and vibrating sample magnetometer (VSM) approved the successful fabrication of MOF with amino arms on its surface besides the well magnetization using magnetic nanoparticles. The MOF/NH2/Fe3O4 composite showed enhanced adsorption capacity (618 mg/g) toward methyl orange (MO) anionic dye which is higher than many commercial reported adsorbents due to the presence of many types of adsorption sites (NH2 groups and lanthanum sites), large surface area of MOF, and the synergetic effect of magnetic nanoparticles. Moreover, the MOF/NH2/Fe3O4 composite showed selective adsorption of MO dye from dye mixtures owing to the electrostatic attraction. Also, the MOF/NH2/Fe3O4 composite retained over 90% of its efficiency for the dye removal even after six successive cycles. So, the present study provided a practical strategy for the design of functional MOF hybrid composites. Furthermore, due to the adaptability of its architectural form, it is a potential adsorbent material for industrial wastewater treatment uses.

Removal of Methylene Blue by Metal Oxides Supported by Oily Sludge Pyrolysis Residues

As a typical pollutant, methylene blue poses a serious threat to the environment and human health. Oily sludge pyrolysis residue loaded with metal oxides could be used to prepare composite materials, which is not only an effective way to treat oily sludge, but also a possible method to treat methylene blue pollutants. In this paper, composite materials (AC-CuO, AC-ZnO, and AC-TiO2) were prepared by oily sludge pyrolysis residue-loaded CuO, ZnO, and TiO2 directly, and characterized by XRD, SEM, EDS, BET, FT-IR, and XPS, and it was shown that the metal oxides were successfully supported on the pyrolysis residue. Then, the composite materials were applied to the removal of methylene blue solution. The removal effect of composite materials on methylene blue with respect to the impregnation time, impregnation ratio and dosage, and the contact time and number of regenerations were investigated, and the removal parameters were optimized by response surface methodology. The removal process for methylene blue was described by applying Lagergren, McKay, Langmuir isotherm, Freundlish isotherm and intraparticle diffusion models. According to the response surface methodology and the main factors affecting the removal effect of methylene blue, the results indicate that the removal effect of 5 mg/L methylene blue could reach 95.28%, 94.95%, and 96.96%, respectively, and the corresponding removal capacities were 4.76, 4.75, and 4.85 mg/g. In addition, kinetic studies showed that the removal process of methylene blue was mainly constituted by chemical adsorption. The intraparticle diffusion showed that the removal of methylene blue may be controlled by both liquid film diffusion and intraparticle diffusion. The isotherms showed that the adsorption sites of composites for methylene blue were uniformly distributed and had the same affinity. Furthermore, regeneration experiments showed that the composite materials were stable and had relatively reusability.

Co3O4 modified polymeric carbon nitride for external light-free chlorine activating degradation of organic pollutants

Advanced oxidation processes (AOPs) activated by chlorine have emerged as a green and efficient strategy for water treatment and have attracted widespread attention. However, most of them require continuous UV radiation during the degradation reaction, which increases the cost and is not conducive to practical application, in some ways. Hererin we proposed an external light-free chlorine activation methodology for the removal of organic pollutants with the assistance of the intrinsic chemiluminescence (CL) in the system. A very interesting phenomenon, 20-fold enhanced CL of Co₃O₄ nanoparticles modified polymeric carbon nitride (PCN/Co₃O₄) was observed in the presence of hypochlorous acid (HClO), compared with the pristine PCN nanosheets. Without ultraviolet (UV), even any other light-emitting devices, the strong intrinsic CL in the PCN/Co₃O₄-HClO system was found to be conducive to chlorine activation degradation of organic pollutants. The inner connection between the CL of the PCN/Co₃O₄-HClO system and the chlorine-based AOPs was further explored.

Nanocoral-like Polyaniline-Modified Graphene-Based Electrochemical Paper-Based Analytical Device for a Portable Electrochemical Sensor for Xylazine Detection

A portable electrochemical device for xylazine detection is presented for the first time. An electrochemical paper-based analytical device (ePAD) was integrated with a smartphone. The fabrication of the ePAD involved wax printing, low-tack transfer tape, and cutting and screen-printing techniques. Graphene ink was coated on the substrate and modified with nanocoral-like polyaniline, providing an electron transfer medium with a larger effective surface area that promoted charge transfer. The conductive ink on the ePAD presented a thickness of 25.0 ± 0.9 μm for an effective surface area of 0.374 cm². This sensor was then tested directly on xylazine using differential pulse voltammetry. Two linear responses were obtained: from 0.2 to 5 μg mL^-1 and from 5 to 100 μg mL^-1. The detection limit was 0.06 μg mL^-1. Reproducibility was tested on 10 preparations. The relative standard deviation was less than 5%. The applicability of the sensor was evaluated with beverage samples spiked with trace xylazine. Recoveries ranged from 84 ± 4 to 105 ± 2%. The developed sensor demonstrated excellent accuracy in the detection of trace xylazine. It would be possible to develop the portable system to detect various illicit drugs to aid forensic investigations.

Synthesis of Polyaniline Supported CdS/CdS-ZnS/CdS-TiO2 Nanocomposite for Efficient Photocatalytic Applications

Photocatalytic degradation can be increased by improving photo-generated electrons and broadening the region of light absorption through conductive polymers. In that view, we have synthesized Polyaniline (PANI) with CdS, CdS-ZnS, and CdS-TiO₂ nanocomposites using the chemical precipitation method, characterized and verified for the photo-degradation of Acid blue-29 dye. This paper provides a methodical conception about in what way conductive polymers “PANI” enhances the performance rate of composite photocatalysts (CdS, CdS-ZnS and CdS-TiO₂). The nanocomposites charge transfer, molar ratio, surface morphology, particle size, diffraction pattern, thermal stability, optical and recombination of photo-generated charge carrier properties were determined. The production of nanocomposites and their efficient photocatalytic capabilities were observed. The mechanism of photocatalysis involved with PC, CZP and CTP nanocomposites are well presented by suitable diagrams representing the exchange of electrons and protons among themselves with supported equations. We discovered that increasing the number of nanocomposites in the membranes boosted both photocatalytic activity and degradation rate. CdS-Zinc-PANI (CZP) and CdS-TiO₂-PANI(CTP) nanocomposites show entrapment at the surface defects of Zinc and TiO₂ nanoparticles due to the demolition of unfavorable electron kinetics, and by reducing the charge recombination, greater photocatalytic activity than CdS-PANI (CP) with the same nanoparticle loading was achieved. With repeated use, the photocatalysts’ efficiency dropped very little, hinting that they may be used to remove organic pollutants from water. The photocatalytic activity of CZP and CTP photocatalytic membranes was greater when compared to CdS-PANI, which may be due to the good compatibility between CdS and Zinc and TiO₂, as well efficient charge carrier separation. PANI can also increase the split-up of photo-excited charge carriers and extend the absorption zone when combined with these nanoparticles. As a result, the development of outrageous performance photocatalysts and their potential uses in ecological purification and solar power conversion has been facilitated. The novelty of this article is to present the degradation of AB-29 Dye using nanocomposites with polymers and study the enhanced degradation rate. Few studies have been carried out on polymer nanocomposites and their application in the degradation of AB-29 dyes and remediation of water purposes. Nanoparticle CdS is a very effective photocatalyst, commonly used for water purification along with nanoparticle ZnS and TiO₂; but cadmium ion-leaching makes it ineffective for practical and commercial use. In the present work, we have reduced the leaching of hazardous cadmium ions by trapping them in a polyaniline matrix, hence making it suitable for commercial use. We have embedded ZnS and TiO₂ along with CdS in a polyaniline matrix and compared their photocatalytic activity, stability, and reusability, proving our nano-composites suitable for commercial purposes with enhanced activities and stabilities, which is a novelty. All synthesized nanocomposites are active within the near-ultraviolet to deep infrared (i.e., 340–850 nm). This gives us full efficiency of the photocatalysts in the sunlight and further proves the commercial utility of our nanocomposites.

Phytic Acid Doped Polyaniline as a Binding Coating Promoting Growth of Prussian Blue on Cotton Fibers for Adsorption of Copper Ions

In recent years, the elimination of heavy metals from wastewater has become an important topic due to rapid industrialization, and it is of considerable interest to develop renewable and degradable materials for this purpose. In this work, a novel Prussian blue/polyaniline@cotton fibers (PB/PANI@CFs) composite was fabricated by a two-step process. Phytic acid doped PANI as a binding coating greatly promoted both the growth of PB and the adsorption of Cu2+. The deposition ratio of PB was as high as 24.68%. Scanning electron microscopy (SEM) displayed that PB nanoparticles were grown more uniformly in the composite and formed a perfect nanocube structure compared with PB@CFs. The successful deposition of both PB and PANI on CFs was demonstrated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FITR), and X-ray photoelectron spectroscopy (XPS). The effect of adsorption time, adsorbent dose, initial pH value, and initial copper sulphate concentration on the adsorption of PB/PANI@CFs composite for Cu2+ was studied by static adsorption and was compared with those of PANI@CFs and PB@CFs. The results showed that the maximum removal efficiency of Cu2+ by PB/PANI@CFs can reach 93.4% within 5 h, and the maximum adsorption capacity of Cu2+ can reach 31.93 mg·g−1. The adsorption of Cu2+ on PB/PANI@CFs followed the pseudo-second order kinetic model and conformed to the Freundlich adsorption isothermal model. The PB-functionalized CFs provided new insights into the design of efficient and low-cost absorbents for heavy metal remediation. The proposed process solves two problems simultaneously, i.e., the utilization of environmentally friendly and biodegradable biomass resources and the adsorption of heavy metal ions, and is a good approach to achieve high-quality and sustainable development.

Polymeric Nanocomposites for Environmental and Industrial Applications

Polymeric nanocomposites (PNC) have an outstanding potential for various applications as the integrated structure of the PNCs exhibits properties that none of its component materials individually possess. Moreover, it is possible to fabricate PNCs into desired shapes and sizes, which would enable controlling their properties, such as their surface area, magnetic behavior, optical properties, and catalytic activity. The low cost and light weight of PNCs have further contributed to their potential in various environmental and industrial applications. Stimuli-responsive nanocomposites are a subgroup of PNCs having a minimum of one promising chemical and physical property that may be controlled by or follow a stimulus response. Such outstanding properties and behaviors have extended the scope of application of these nanocomposites. The present review discusses the various methods of preparation available for PNCs, including in situ synthesis, solution mixing, melt blending, and electrospinning. In addition, various environmental and industrial applications of PNCs, including those in the fields of water treatment, electromagnetic shielding in aerospace applications, sensor devices, and food packaging, are outlined.

Preparation of Magnetic Composite Polyaniline/Fe3O4−Hydrotalcite and Performance in Removal of Methyl Orange

Magnetic composite fabricated from polyaniline and Fe3O4-hydrotalcite (Pan/MHT) was successfully applicated for removal of methyl orange (MO) from wastewater. The structure and properties of Pan/MHT were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer, and Brunauer-Emmett-Teller adsorption isotherm. Adsorption kinetic results indicated that the adsorption process followed pseudosecond-order kinetic model ( $R^2=0.999$ ), MO adsorption onto Pan/MHT was well described by Freundlich isotherm ( $R^2=0.994$ ), and the MO adsorption capacity of 2 Pan/MHT obtained the highest with $Q_e=156.25\text{mg}/\text{g}$ . Batch adsorption experiments were carried out using magnetic composite with the effects of initial MO concentration, solution pH, and adsorbent dosage. The results revealed that the magnetic Pan/MHT exhibited efficient adsorption of MO in the aqueous solution as a result of the affinity for organic dyes, microporous structure, and suitable surface area for adsorption (15,460 m2/g). The superparamagnetic behavior of Pan/MHT (with $H_c=18.56\text{Oe}$ , $M_s=23.38\times {10}^{-3}\text{emu}/\text{g}$ , and $M_r=0.91\times {10}^{-3}\text{emu}/\text{g}$ ) helps that it could be separated from the solution and performs as an economical and alternative adsorbent to removal and degrade azo dye from wastewater. Pan/MHT was also investigated to reuse after desorption of MO in 0.1 M HCl, and the results show that 2 Pan/MHT can be reused for 4 cycles with $Q_e=79.66\text{mg}/\text{g}.$

Efficient heavy metal removal from water by alginate-based porous nanocomposite hydrogels: The enhanced removal mechanism and influencing factor insight

Novel porous alginate-based nanocomposite hydrogels were prepared by incorporating polyaniline-polypyrrole modified graphene oxide (GO@PAN-PPy) as reinforcing fillers into the alginate matrix (GO@PAN-PPy/SA) for Cr(VI) and Cu(II) removal from water. Different in-situ co-polymerization functionalized GO with Py-to-An mass ratios of monomers (from nil to 1:1) and contents of GO@PAN-PPy (from nil to 2.0%(w/v)) were embedded into the alginate backbone to improve the sorption performance. Key factors, such as pH, coexisting metal ions, and swelling states were investigated in batch adsorption modes. The synergistic effect combined from polymer backbone and fillers could lower the impact of the pH-dependent adsorption reaction. With an adsorption ability superior to that of plain SA and GO/SA, the optimized GO@PAN-PPy-2(1)/SA exhibited good experimental maximum adsorption capacities for Cr(VI) (~133.7 mg/g) and Cu(II) (~87.2 mg/g) at pH 3.0, which were better than those of many other similar sorbents. The sorbents possessed excellent adaptability for 0.2 M salt for Cr(VI) removal but poor for Cu(II) removal. Pre-swelling treatment and co-adsorption could enhance the adsorption performance. The excellent reusability of hydrogel was demonstrated after five cycles in single/binary system. Overall, this work reveals that the resultant hydrogel holds potential as candidate sorbent to remove anionic-cationic heavy metal ions from water.

Polyaniline/Nanomaterial Composites for the Removal of Heavy Metals by Adsorption: A Review

Heavy metals represent one of the most important kinds of pollutants, causing serious threats to the ecological balance. Thus, their removal from aqueous solution is a major environmental concern worldwide. The process of adsorption—being very simple, economical, and effective—is widely applied for the decontamination of wastewaters from heavy metals. In this process, the adsorbent is the key factor affecting the performance; for this reason, significant efforts have been made to develop highly efficient and selective adsorbents with outstanding properties. This paper presents a detailed overview of the research on different methods of synthesis of nanocomposite materials based on the polymer polyaniline combined with nanomaterials, along with the influence of the synthesis method on their size, morphology, and properties. In addition, the study evaluates the adsorption efficiency of various developed nanocomposites for the adsorption of heavy metals from aqueous solution. From an economical and environmental point of view, the regeneration studies of the nanocomposites are also reported.

Photocatalytic Treatment of Wastewater Containing Simultaneous Organic and Inorganic Pollution: Competition and Operating Parameters Effects

In the present study, methylene blue (MB) removal from aqueous solutions via the photocatalytic process using TiO2 as a catalyst in the presence of external ultra-violet light (UV) was investigated. The results of adsorption in the absence of UV radiation showed that adsorption reached an equilibrium state at 60 min. The experimental kinetic data were found to be well fitted by the pseudo-second-order model. Furthermore, the isotherm study suggested that dye uptake by TiO2 is a chemisorption process with a maximum retention capacity of 34.0 mg/g. The photodegradation of MB was then assessed under various experimental conditions. The related data showed that dye mineralization decreased when dye concentrations were increased and was favored at high pH values and low salt concentrations. The simultaneous presence of organic and inorganic pollution (Zinc) was also evaluated. The effect of the molar ratio Zn2+/MB+ in the solution at different pH values and NaCl concentrations was also monitored. The corresponding experimental results showed that at low values of Zn2+ in the solution (30 mg/L), the kinetic of the MB removal became faster until reaching an optimum at Zn2+/MB+ concentrations of 60/60 mg/L; it then slowed down for higher concentrations. The solutions’ carbon contents were measured during the degradation process and showed total mineralization after about 5 h for the optimal Zn2+/MB+ condition.

Nanomodified sugarcane bagasse biosorbent: synthesis, characterization, and application for Cu(II) removal from aqueous medium

Biosorption is a technique widely used in the remediation of contaminated effluents, and its main advantages are its easy applicability, high efficiency rate, versatility, and its economic viability. Associated with nanotechnology, this work proposes the use of nanocomposites of sugarcane bagasse (SB) and ferromagnetic nanoparticles (Fe₃O₄) in the removal of metallic ions present in contaminated water. SB is a promising adsorbent material since it is an abundant agricultural residue, easily accessed. By using the coprecipitation method, two nanocomposites were obtained from in natura (SB-NP) or acid-treated (MSB-NP) sugarcane bagasse. These materials were synthetized by impregnation of Fe₃O₄ to gain paramagnetic properties and to facilitate the removal of the contaminant-containing adsorbent. The characterization of the nanocomposites was performed using pH_PCZ, FTIR, XRD, and SEM/EDS techniques, to evaluate the synthesis efficiency and investigate the morphology of the materials. The efficiency of magnetite impregnation on the SB was assessed by SEM/EDS and XRD, while the main functional groups (carbonyl, carboxyl, hydroxyl, amine, amide, and nitrate) responsible for adsorption were found by FTIR. In the surface charge characterization by pH_PCZ sorption of dyes, it was found that negative charges are predominant. The pH_PCZ for SB-NP and MSB-NP was 5.95 and 5.59, respectively, and the chosen Cu(II) adsorption pH was 6.2 ± 0.1. The adsorption equilibrium was reached between 10 and 60 min of contact time. The maximum experimental sorption capacity (SC_exp) was 2.53 ± 0.09 (SB-NP) and 2.61 ± 0.01 mg/g (MSB-NP). The isotherm models applied to the experimental data were Langmuir, Freundlich, Sips, Temkin, and Dubinin-Radushkevich, and Temkin best described the adsorption phenomena for Cu(II) by SB-NP (r² = 0.9976 and χ² = 3.965) and MSB-NP (r² = 0.9990 and χ² = 1.816). Reuse cycles of the nanocomposites were also performed employing ten cycles of sorption using 50 mg/L Cu(II) solutions, after which the materials showed SC_exp = 7.47 ± 0.04 mg/g (SB-NP) and 7.82 ± 0.04 mg/g (MSB-NP). Therefore, the investigated materials exhibited promising results to be used as biosorbents in the remediation of effluents contaminated with toxic metal ions, such as copper.

Green synthesis of poly(pyrrole methane) for enhanced adsorption of anionic and cationic dyes from aqueous solution

The presence and accumulation of dyestuff in the environment is posing great harm to human beings. In this study, a novel poly(pyrrole methane) (PPm) adsorbent with abundant OH was greenly synthesized via a facile polymerization method. Its physicochemical properties were characterized in detail. Furthermore, the adsorption performance of PPm for anionic dye (acid red G, ARG) and cationic dye (methylene blue, MB) was comparatively studied with a typical dye adsorbent (polyprrrole, PPy). The results revealed that the adsorption of ARG or MB onto PPm followed pseudo-second-order model and Langmuir mode. The adsorption processes were endothermic and spontaneous. The maximum capacities of PPm to adsorb ARG and MB were 555.56 mg/g and 99.11 mg/g, which were about 10 and 2 times higher than that of PPy, respectively. PPm could be reused for 5 cycles without a significant decrease of its adsorption rate. The adsorption of ARG and MB is mainly attributed to electrostatic interaction and hydrogen bonding between ARG or MB and OH in PPm. Additionally, ARG could be adsorbed by ion exchange with the doped Cl^- in PPm. Therefore, this study provides a new strategy to synthesis efficient adsorbent for the removal of both anionic and cationic dyes.

Rapid and efficient removal of diclofenac sodium from aqueous solution via ternary core-shell CS@PANI@LDH composite: Experimental and adsorption mechanism study

The efficient removal of Diclofenac sodium (DCF), a nonsteroidal anti-inflammatory drug, has attracted more and more attention. In this work, ternary core-shell CS@PANI@LDH composite was synthesized via the in-situ growth of Mg/Al layered double hydroxide plates onto polyaniline-wrapped carbon sphere and applied for DCF removal. Various influence factors like concentration, pH, time, temperature, and background electrolytes were systematically investigated. The maximum adsorption capacity was 618.16 mg/g. Besides, after 5 regeneration cycles, CS@PANI@LDH still retained high adsorption capacity. The adsorption mechanism was investigated by Fourier transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) characterization analyses. Simultaneously, the Multiwfn program combined the Chimera program was applied to calculate and visualize the localized orbit locator (LOL) of π electrons in DCF^- molecule, which explored the π electronic structure and conjugation characteristics of DCF^- molecule. Moreover, the Independent Gradient Model (IGM) analysis based on pro-molecular density revealed the interaction sites and interaction strength between DCF and LDH. The adsorption mechanism could be explained through electrostatic interaction and hydrogen bonding between LDH and DCF, π-π interaction between DCF and PANI. It was the synergistic effects of different interactions that improved the adsorption of DCF by CS@PANI@LDH composite.

Polyaniline–niobium oxide nanohybrids with photocatalytic activity under visible light irradiation

In this study, we reported the production of polyaniline and niobium oxide hybrids synthesized by the direct reaction between a niobium peroxyoxalate complex and anilinium salt in an aqueous medium.