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Novel NaCoxOy adsorbents were fabricated by air calcination of (Na,Co)-organic frameworks at 700 °C. The NaCoxOy crystallized as hexagonal microsheets of 100–200 nm thickness with the presence of some polyhedral nanocrystals. The surface area was in the range of 1.15–1.90 m2 g−1. X-ray photoelectron spectroscopy (XPS) analysis confirmed Co2+ and Co3+ sites in MOFs, which were preserved in NaCoxOy. The synthesized adsorbents were studied for room-temperature H2S removal in both dry and moist conditions. NaCoxOy adsorbents were found ~ 80 times better than the MOF precursors. The maximum adsorption capacity of 168.2 mg g−1 was recorded for a 500 ppm H2S concentration flowing at a rate of 0.1 L min−1. The adsorption capacity decreased in the moist condition due to the competitive nature of water molecules for the H2S-binding sites. The PXRD analysis predicted Co3S4, CoSO4, Co3O4, and Co(OH)2 in the H2S-exposed sample. The XPS analysis confirmed the formation of sulfide, sulfur, and sulfate as the products of H2S oxidation at room temperature. The work reported here is the first study on the use of NaCoxOy type materials for H2S remediation.

Rapid industrialization is deteriorating air and water quality by exposing life to a wide range of pollutants, thus calling for efficient and affordable remediation strategies. Metal–organic frameworks (MOFs) are emerging materials for environmental remediation applications due to their high surface area, ordered porous structure, and application-specific tailoring of properties. In particular, transition metal-based frameworks are advanced adsorbents and catalysts for the remediation of organic and gaseous pollutants. Physicochemical properties are mainly dependent on the choice of the metal center, the oxidation state, and organic linkers. Bimetallic-, polyoxometalate-, and metal oxide-incorporated frameworks find applications as photocatalysts for decontamination of dyes, phenolic compounds, pesticides and pharmaceutical drugs under ultraviolet (UV)/visible radiations. Large surface area coupled with high activity of transition metal frameworks allows the capture and removal of inorganic and volatile organic pollutants. Transition metal frameworks convert gaseous pollutants into value-added chemicals. Frameworks containing synthetic and natural fibers are currently studied to remove chemical warfare agents.

In this study, we report a surfactant-mediated synthesis of ferrites (MFe2O4: M = Co, Ni, Cu, Zn) using the co-precipitation-oxidation method. The band gap calculated from UV-Visible diffuse reflectance spectra were found in the range of 1.11–1.81 eV. These ferrite nanocatalysts were studied for the photocatalytic degradation of multiple organic dyes in a 32 W UV-C/H2O2 system. All the four ferrites showed an excellent dye degradation rate in the range of 2.065–2.417 min−1 at neutral pH. In the optimized condition, NiF was found to degrade 89%, 92%, 93%, and 78% of methylene blue, methyl orange, bromo green, and methyl red, respectively within 1 min of UV-irradiation. A 40% TOC removal was recorded after 5 min of degradation reaction, which increased to 60% after 50 min. Mechanism elucidated by scavenger studies and fluorescence spectroscopy revealed that •OH and holes were the primary reactive radicals responsible for the degradation process. Ferrite photocatalysts showed an insignificant performance loss in seven consecutive cycles. The photocatalyst was found efficient in the presence of a high concentration of salts. Thus, it was concluded that these photocatalysts are highly suitable for the remediation of dye-contaminated wastewater.

We have reported the fabrication of NaMnxOy from air calcination of (Na,Mn)-organic frameworks. The hexagonal microsheets of NaMnxOy formed irrespective of the type of organic linker or MOF morphology. The adsorption capacity of NaMnxOy was found 40–70 times higher than the precursor MOF. The best adsorbent showed the maximum adsorption capacity of 818.7 and 116.3 mg g−1 in wet and dry condition, respectively. The experimental parameters like mass of adsorbent and flow rate played a decisive role in the adsorption capacity. X-ray diffraction and photoelectron spectroscopy analyses predicted NaMnxSy, S, and MnSO4 as the reaction products. The spent adsorbent was stripped with an ammonia solution to yield ammonium sulfate (liquid fertilizer) and regenerated adsorbent. The regenerated adsorbent retained an adsorption capacity of more than 110 mg g−1 in the fourth cycle. It is the first report of NaMnxOy formation from the MOF precursor.

Oil/water separation is an important issue in the environmental field because of increasing worldwide oil pollution. In particular, emulsion under 20 μm in size causes a serious problem in water treatment. Thus, development of an effective oil/water emulsion separation membrane is required. Asymmetric wettability is one effective technique for emulsion separation due to its directional liquid transport property. In this research, wettability was controlled by adjusting the diameter of an electrospun nanofiber for a difference in surface roughness. Through analysis of the surface structure and contact angle of nanofibers with various diameters, the contact angles of fibers with different diameters were increased about 40° to confirm that surface structure affects surface wettability. Comparison of asymmetric wettability membranes (AwENMs) and a single membrane (ENM) for oil/water emulsion separation shows that AwENMs perform about two times faster and reject 10% of emulsion.

In this study, electrospun nanofiber was continuously sandwiched between two rubber rollers at high temperature (150 °C). The prepared nanofiber support layer possessed a pore size of 0.4 μm (with narrow distribution) and a fiber diameter of 292 ± 94 nm. Afterward, an interfacial polymerization was employed to deposit the selective polyamide layer on the nanofiber support layer. For the first time, engineered osmosis (EO) was used as a platform for verifying the presence of a polyamide selective layer on a nanofiber support layer. We found that the membrane prepared exhibited an excellent combination of permeability (30 L/m2h) and selectivity (17 g/m2h and 0.57 g/L) under a net pressure of 49 bar at the EO platform. The membrane developed can be applied to generate renewable energy using the EO process. In addition, the EO method can be used to detect selective polymer having a nano-scale thickness.

The development of efficient adsorbents for environmental applications has been prioritized, considering the increasing pollution worldwide. The continuous search for new and effective materials has led to the development of polyamidoamine (PAMAM) dendrimer-based materials for their use in wastewater treatment, precious metal recovery, sensing, and CO2 capture. PAMAM with a three-dimensional branched architecture, accessible internal cavities, and easy surface functionalization are suitable for removing inorganic (radionuclides, heavy metals, and precious metal ions) and organic (dyes, drugs, and pesticides) pollutants. Moreover, a large number of terminal amines of PAMAM dendrimer serve as a suitable platform for CO2 capture and conversion. This review is intended to provide the readers with an updated overview of PAMAM-based adsorbents and their role in the removal and recovery of various inorganic and organic pollutants. PAMAM-based materials as a sensor for pollutants detection and quantification has been discussed. Also, environmental considerations related to the use of PAMAM-based materials have been included.

In this work, a piezoelectric electrospun nanofiber membrane (pENM) was prepared to confirm its antifouling ability through the vibrational inducement of fluid instability. For the optimization of the pENM properties, the synthetic conditions (solvent ratio, tip-to-collector distance (TCD), and heat treatment time) were adjusted. The optimized properties were observed at a 5/5 acetone/N-methyl-2-pyrrolidone (NMP) solvent ratio, a TCD of 20 cm, and a heat treatment time of 0.5 h. The optimized pENM exhibited three times higher water permeability (5573 LMH/bar) and rejection performance (99.87%) for particulates than a commercial microfiltration (MF) membrane. The flux decline was reduced by 15% in the presence of a piezoelectric effect when compared to the flux decline in the absence of a piezoelectric effect. This result shows that the pENM has potential for water-treatment applications.

In this study, we compared the performances of three iron-containing crystalline and amorphous catalysts, that is, Fe-Zeo-A, Fe-ZSM-5, and Fe-silica, respectively, for the degradation of phenol in an aqueous solution. Catalytic activity for the degradation of phenol was assessed by heterogeneous photolysis, Fenton, and photo-Fenton oxidation. All catalysts exhibited higher activity in the photo-Fenton process. In addition, the catalyst stability was evaluated by the estimation of the iron loss and structural variations after the oxidation processes. Results revealed that Fe-silica and Fe-ZSM-5 exhibit higher catalytic activity (~100% phenol removal), while only 64% of phenol removal over Fe-Zeo-A was observed. Moreover, among all catalysts, Fe-ZSM-5 exhibited higher stability with low iron leaching, attributed to the uniform distribution of bonded Fe in the crystalline framework and narrow channels. On the contrary, amorphous Fe-silica exhibited higher iron leaching due to the presence of isolated iron species in the structure, leading to the partial involvement of a homogeneous reaction during the degradation of phenol. The structural stability of Fe-based catalysts was examined using microscopic and spectroscopic techniques.

A mixed ligand Cu-based MOF, Cu(BDC)0.5(BDC-NH2)0.5 was synthesized by a rapid ultrasonication method for the adsorptive removal of hydrogen sulfide (H2S) gas at room temperature. The MOF has a sheet-like morphology with 100 nm thickness crystallized in the monoclinic symmetry (a = 11.27 A, b = 14.82 A, c = 7.95 A, β = 110.8°) with C2/m space group. The surface area and pore volume was 19.4 m2 g−1 and 0.024 cm3 g−1, respectively. The XPS analysis confirmed a near equal proportion of Cu(I) and Cu(II)-sites in the MOF. The MOF showed the H2S adsorption capacity of 128.4 mg g−1 for 500 ppm of H2S flowing at a rate of 100 mL min−1, which is among the highest values reported for Cu-based MOFs. The spent MOF was regenerated by a methanol and UV-irradiation method, which significantly improved the adsorption capacity. The H2S adsorbed onto the MOF by breaking Cu-carboxylate bonds with the formation of covellite CuS nanoparticles and sulfates. The spectroscopic analysis predicted a Cu(OH)-type sites after UV-irradiation along with increased surface area, which were responsible for an enhanced adsorption capacity of the regenerated sample.

A new and facile one-step synthesis method for preparing granulated mesoporous carbon (GMC) with three-dimensional spherical mesoporous symmetry is prepared to remove large molecular weight organic compounds in aqueous phase. GMC is synthesized in a single step using as-synthesized mesoporous carbon particles and organic binders through a simple and economical synthesis approach involving a simultaneous calcination and carbonization process. Characterization results obtained from SEM, XRD, as well as surface and porosity analysis indicate that the synthesized GMC has similar physical properties to those of the powdered mesoporous carbon and maintains the Brunauer-Emmett-Teller (BET) surface area and pore volume because the new synthesis method prevents the collapse of the pores during the granulation process. Batch adsorption experiments revealed GMC showed a substantial adsorption capacity (202.8 mg/g) for the removal of methyl violet as a target large molecular contaminant in aqueous phase. The mechanisms and dynamics modeling of GMC adsorption were also fully examined, which revealed that surface diffusion was rate limiting step on adsorption process of GMC. Adsorption kinetics of GMC enables 3 times faster than that of granular activated carbon in terms of surface diffusion coefficient. This is the first study, to the best of our knowledge, to synthesize GMC as an adsorbent for water purification by using facile granulation method and to investigate the adsorption kinetics and characteristics of GMC. This study introduces a new and simple method for the synthesis of GMC and reveals its adsorption characteristics for large molecular compounds in a water treatment.

The influence of the electrospinning parameters on the diameter of the polyethersulfone (PES) nanofibers was demonstrated using response surface methodology. The electrospinning parameters studied were lithium chloride (LiCl) concentration, PES concentration, feed rate, and tip-to-collector distance. The average fiber diameter was correlated to these factors by using a second-order polynomial function at a 95% confidence level. The statistical analysis indicated that LiCl concentration, PES concentration, and feed rate had the significant connection with the fiber diameter, and LiCl concentration was the most important factor in determining the fiber diameter. When LiCl concentration increased, the fiber diameter decreased, because with more LiCl that is added, more applied voltage is needed to overcome the electrostatic attractions. The interactive effect between PES concentration and feed rate, the interactive effect between PES concentration and tip-to-collector distance, and the quadratic coefficients of LiCl concentration were also found to be significant. The adjusted determination coefficient (Radj2) of the model was calculated to be 0.9106. The water flux measurements showed that the decrease in the fiber diameter of the membrane caused the decrease in the initial pure water flux. The retention tests with 0.6 &mu, m polystyrene (PS) suspension indicated that as the fiber diameter decreased, the pore sizes decreased and the particle removal efficiency increased.

In this study, a novel coral-like Fe2O3/Mn2O3 nanocomposite (FMNC) was synthesized by a one-step surfactant-mediated co-precipitation method. The application of this material was demonstrated for the degradation of organic dyes. The crystallographic analysis of FMNC confirmed the presence of α-Fe2O3 and α-Mn2O3 with no impurity of MnFe2O4. The photocatalyst showed strong absorbance in the UV and Visible range with a low bandgap energy of 1.11 eV. In the optimized experimental conditions (0.5 g L−1 photocatalyst, 10 mg L−1 MB concentration, and 5 mmol L−1 H2O2), the FMNC photocatalyst showed 80–97% degradation of organic dyes within 75 s using low power UV-C irradiation. Moreover, scavenger studies confirmed the involvement of OH radicals and holes as the main active species responsible for the dye degradation process. The photocatalytic degradation process was insignificantly affected by the presence of inorganic anions. The photocatalyst showed a ~ 5% loss of performance after seven photocatalytic cycles. This study concluded that UV/H2O2/FMNC system is a fast, efficient, and economical approach for remediation of dye-contaminated wastewater.

The application of electrospun nanofiber membranes (ENMs) as microfilters for the process of water purification requires the substrate to possess suitable strength, permeability, and a smooth surface. Therefore, the fiber homogeneity, inter-fiber adhesion, and surface roughness of the ENMs must be carefully controlled. Concurrently, an understanding of the ENMs' rejection mechanism for contaminants is necessary for the effective application of ENMs. In this study, we demonstrate the fabrication of polyethersulfone (PES) ENMs, which are useful for water purification as water treatment membranes. An optimum fabrication condition that can significantly improve the mechanical property and surface roughness of the PES membrane is also illustrated. This technique induces the solvent remaining on the fiber's surface after the electrospinning process, and the mechanical properties and surface roughness of the membrane are improved by the solvent-induced fusion of the fiber. The fabricated PES ENMs also show higher clean water productivity. Additionally, we show that a particulate contaminant in water is mainly rejected on the ENM surface by using a water filtration test. Based on our conclusions, we suggest the appropriate ENM regeneration method and confirm that the fabricated ENMs show excellent regeneration ability.