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MOF-199 is one of the well-studied metal–organic frameworks (MOFs) for the capture of small gas molecules. In this study, we have investigated the thermal transformation of MOF-199 microrods to CuO nanoparticles by various microscopic and spectroscopic techniques. The growth of oxide was initiated by the formation of ∼2.5 nm particles at 200 °C, which ended up as CuO nanoparticles of ∼100–250 nm size at 550 °C. An intermediate presence of Cu2O along with CuO was recorded at 280 °C. The MOF and calcined products were tested for the room-temperature desulfurization process. MOF-199 showed the maximum adsorption capacity for H2S gas (77.1 mg g–1) among all adsorbents studied. Also, MOF-199 showed a better regeneration efficiency than the derived oxide. For a sustainable process, the exhausted adsorbents were used for the photocatalytic degradation of methylene blue. The exhausted materials showed better degradation efficiencies than the fresh materials. This study reports new sustainable approaches for MOF-199 application in air and water decontamination.

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.

Here, we have fabricated a bimetallic Ag–Cu-trimesate metal–organic framework at room temperature. The MOF showed rod-like morphology with a uniform distribution of Ag and Cu-sites in the MOF. The MOF has a surface area of 27.2 m2 g−1 with a mean pore diameter of 3.8 nm. The X-ray photoelectron (XPS) analysis confirmed the presence of Ag(I), Cu(I), and Cu(II) sites in the MOF. Moreover, a minor fraction of Ag as Ag0 (27.2%) was confirmed due to the reductive effect of DMF solvent. The synthesized MOF was tested for H2S removal under ambient conditions, where a maximum adsorption capacity of 69.7 mg g−1 was achieved. A novel regeneration method based on H2O2 solution partially regenerated the MOF. The diffraction pattern predicted the exceptional stability of the MOF after the adsorption–regeneration process. The XPS analysis confirmed sulfate/bisulfate (82.6%) and sulfide (17.4%) as the H2S adsorption/oxidation species. The regeneration process involved the oxidation of Ag0 and Cu(I), which resulted in appreciable adsorption capacity in the subsequent cycles. Thus, we have reported a new and economical synthesis of bimetallic MOFs and a method for the partial regeneration of the spent MOF.

In this study, CeO2/Fe2O3, CeO2/Mn2O3, and CeO2/Mn2O3/Fe2O3 nanocomposites were synthesized by the calcination of molten salt solutions. The microscopic images confirmed polyhedral nanocrystals of 10–20 nm size, clustered to form nanospheres. The elemental mapping confirmed the uniform distribution of transition metal oxides in the CeO2 matrix. The X-ray diffraction analysis confirmed the phase purity of metal oxides in nanocomposites. The surface area of nanocomposites was in the range of 16–21 m2 g−1. X-ray photoelectron spectroscopy confirmed 25–28% of Ce3+ ions in the CeO2 of nanocomposites. These nanocomposites were tested for the removal of hydrogen sulfide gas at room temperature. The maximum adsorption capacity of 28.3 mg g−1 was recorded for CeO2/Mn2O3/Fe2O3 with 500 ppm of H2S gas and 0.2 L min−1 of flow rate. The adsorption mechanism probed by X-ray photoelectron spectroscopy showed the presence of sulfate as the only species formed from the oxidation of H2S, which was further confirmed by ion chromatography. Thus, the study reports room-temperature oxidation of H2S over mixed metal composites, which were synthesized by a novel one-step approach.

Three copper-based metal–organic frameworks (MOFs) with different organic linkers were synthesized for the removal of H2S gas at room temperature. The synthesized MOFs were characterized by microscopic and spectroscopic techniques to understand their structural, functional, and optical properties. The H2S adsorption capacity of MOFs calculated by column studies followed the trend: 105.6 mg g−1 (CuBDC) > 27.1 mg g−1 (CuBTC) > 1.3 mg g−1 (CuBDC-N) in dry conditions. The adsorption capacity increased in moist conditions due to an easy dissolution and dissociation of H2S in a film of water. X-ray photoelectron spectroscopy confirmed the presence of sulfur bound to Cu-sites and sulfate ions. The spent MOFs were regenerated by the successive effect of methanol and low power UV-C radiation. The regenerated CuBTC showed an exceptionally high adsorption capacity of 95.6 mg g−1 in the second cycle, which was linked to the reactivation of Cu-sites and improved surface area and porosity. The regeneration process developed in this study is a cost-effective method to recycle chemisorbed MOFs without compromising with their structural and functional integrity.

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.

The performance of UV-activated Fe2O3-containing ZSM-5 (UFZ5) and silica (UFS) as adsorbents for the removal of low concentration of volatile organic sulfur compounds (VOSCs) was investigated in ambient conditions. A ∼99.9% and ∼89.2% removal of 10 ppm DMDS was observed for UFZ5 and UFS, respectively, due to a higher proportion of iron in UFZ5. The N2 adsorption isotherm confirmed an unpredictable increase in the surface area and pore volume of adsorbents after the fifth adsorption-oxidation cycle, which made adsorbents highly reusable for multiple cycles. The spectroscopic analysis predicted an increase in the hydroxyl density along with the resistance of catalytic sites against sulfur deactivation, which favored the adsorption-oxidation process. The adsorption capacity of UFZ5 remained in the range of 0.12–0.22, 0.26–0.48, 0.40–0.75 mg g−1 for methyl mercaptan (MM), dimethyl sulfide (DMS), and dimethyl disulfide (DMDS), respectively which were significantly higher than those calculated for UFS. The analysis confirmed SO2, CO, CH3OH, H2O, and elemental S as by-products. The UFZ5 was found competent and robust for the treatment of VOSCs-contaminated indoor air.

This work reported the fabrication of NaMxOy-type adsorbents from air calcination of (Na, M)-trimesate metal-organic frameworks. NaMnxOy (NMO) crystallized as disc-shaped microsheets, whereas NaCoxOy (NCO) crystallized as smooth microsheets with surface deposition of polyhedral nanoparticles. The oxides have a surface area of 1.90–2.56 m2 g−1. The synthesized adsorbents were studied for low-temperature SO2 removal in breakthrough studies. The maximum adsorption capacity of 46.8 mg g−1 was recorded for NMO at 70 °C. The adsorption capacity increased with the increasing temperature due to the chemisorptive nature of the adsorption process. The capacity increased with the increasing bed loading and decreasing flow rate due to the improved SO2 retention time. The elemental mapping confirmed the uniform distribution of sulfur species over the oxide surface. X-ray diffraction showed the absence of metal sulfate nanoparticles in the SO2-exposed samples. The X-ray photoelectron analysis confirmed the formation of surface sulfate and bisulfate. The formation of oxidized sulfur species was mediated by hydroxyl groups over NMO and lattice oxygen over NCO. Thus, the work demonstrated here is the first such report on the use of NaMxOy-type materials for SO2 mineralization.

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.

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.

We have reported iron-based MOFs by sonication of organic linkers with a freshly prepared iron hydroxide, which served as templates to yield iron oxide adsorbents after calcination. The PXRD analysis confirmed the presence of α-Fe2O3 and Na2SO4 in MOF-derived adsorbents. The XPS analysis confirmed the presence of both Fe2+ and Fe3+ species in all MOFs and derived iron oxide adsorbents. These adsorbents were studied for H2S removal in both dry and moist conditions at room temperature. The iron terephthalate MOF-derived iron oxide adsorbent showed the maximum adsorption capacity of 36.2 mg g−1 at moist conditions. The H2S removal process over iron oxide adsorbents was governed by the oxidation of H2S into sulfur and sulfates by Fe3+ and adsorbed oxygen. The spent adsorbent was regenerated by NH4OH to produce ammonium sulfate (liquid fertilizer), which is a novel approach to convert waste into value-added products.

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.

Zn-MOF/ZnO nanocomposites with different organic linkers were fabricated by a rapid ultrasonication method using freshly prepared Zn(OH)2 precipitate. The high metal-to-ligand ratio led to the simultaneous formation of MOFs and ZnO nanoparticles in the MOFs. The surface area was in the range of 12–21 m2 g−1. The nanocomposites were tested for H2S adsorption at room temperature, where the maximum adsorption capacity of 14.2 mg g−1 was recorded for ZnBTC/ZnO in dry conditions. The spent adsorbents were regenerated using methanol and UV irradiation as individual and combined strategies. The successive effect of methanol and UV radiation led to an increased adsorption capacity in the second cycle. The spectroscopic investigation of spent ZnBDC/ZnO confirmed the chemisorption of H2S over Zn-sites via Zn2+−S2− interaction. The XPS analysis of regenerated ZnBDC/ZnO confirmed a decreased sulfur content and decreased Zn ionic character. The regeneration work in this study is one of the first attempts and could be extrapolated to well-studied Zn-MOFs like MOF-5 for the desulfurization process.

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.

In this study, Fe-Zeolite-A as a phosphate adsorbent was synthesized by incorporating iron into the framework of Zeolite-A using ammonium iron citrate as the Fe3+source. The adsorption (in acidic condition) and desorption of phosphate (in alkaline condition) from an aqueous solution was repetitively performed for 18 times in batch test using Fe-Zeolite-A. The rate of adsorption and desorption of PO43- was much faster (consistently) than any of the reported study so far. The crystalline phase of pristine zeolite changed to amorphous after one adsorption phase and ultimately transformed into a highly amorphous phase after 18 adsorption/desorption cycles. It was due to the formation of more active sites on the surface of the zeolite by a release of atoms, breaking of bonds and deposition of metal and phosphate compounds on the surface (by rigorous acid/base treatment). Increase in active sites enhanced the sorption efficiency of Fe-Zeolite-A. With the help of microscopic and spectroscopic techniques, it was found that Fe3+, Al3+and Na+ metal ions of the Fe-Zeolite-A were involved in the adsorption/desorption of PO43-. Fe3+ ion exhibited ligand exchange mechanism by exchanging OH ions with PO43-. Al3+and Na+ exhibited interactions like precipitation, hydrogen bonding, and diffusion respectively to adsorb PO43-. Fe3+ metal ion dominated over other metal ions by ligand exchange principle, making the sorption process a highly reversible one. The adsorbent showed quantitative adsorption/desorption capacity even after continuous 18 cycles indicating a higher level of reusability.

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.

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.

This study reported a surfactant-mediated synthesis of coral-like α-Fe2O3 nanoparticles (FONP) via a simple co-precipitation-oxidation route. The synthesized FONP photocatalyst had a hexagonal morphology, as observed in the transmission electron micrographs. A surface area of 15 m2 g−1 was calculated from the N2 adsorption-desorption isotherm. The photocatalyst showed strong absorbance in the entire UV–Visible range with a low bandgap energy of 1.91 eV as estimated using the Tauc plot. The photocatalytic activity of FONP was evaluated by degrading several organic dyes at neutral pH. In the optimized experimental conditions, the FONP photocatalyst showed fast degradation of Methylene blue (95%), Methyl orange (94%), Bromo green (94%), and Methyl red (76%) within 5 min in 32 W UV/H2O2 system. The reusability study showed a 10% loss in the degradation efficiency after five cycles. A possible photo-Fenton degradation mechanism was deduced based on scavenger studies.

Here, we have investigated the effect of UV-pretreatment on the physicochemical properties of an adsorbent. The UV-irradiated Fe-incorporated ZSM-5 (UV-FZ5) showed structural and chemical changes arising due to UV-cleaving of framework bonds resulting in a decreased crystallinity and change in the local environment of Fe species. More visible modifications were observed for UV-irradiated iron-containing silica (UV-Fe/AS) where silica network reconfiguration, increased hydroxyl density, and change in the Fe coordination were estimated. A 0.5–81.2% increase in BTEX adsorption was recorded for UV-irradiated adsorbents. These hiked performances were attributed to the increased pore size, increased hydroxyl density, and formation of newer isolated Fe3+ framework species. For FZ5, adsorption occurred via size-selective diffusion followed by hydrogen bonding and cation-pi interaction, whereas, for Fe/AS, diffusion was followed by cation-pi interactions. Moreover, adsorbents retained their adsorption capacity for multiple cycles and were found economically suitable for treating VOCs-contaminated air.