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 NaCo_xO_y adsorbents were fabricated by air calcination of (Na,Co)-organic frameworks at 700 °C. The NaCo_xO_y 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 NaCo_xO_y. The synthesized adsorbents were studied for room-temperature H₂S removal in both dry and moist conditions. NaCo_xO_y 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 NaCo_xO_y type materials for H₂S remediation.

Bimetallic Ag-Cu-trimesate metal-organic framework was fabricated for H ₂ S mineralization. The MOF was partially regenerated using H ₂ O ₂ solution for five cycles.

In an effort to explore the potential for the removal of arsenic from water, mesoporous iron oxide (MI) was prepared using a sonochemical method. The surface area and average pore size of the MI sample were determined using a Brunauer Emmett Teller (BET) analysis to be 269 m²/g and 6.9 nm, respectively. Kinetic experiments revealed that more than 90% of the As(III) and As(V) were adsorbed onto the MI sample within 5 min at 0.1 g/L of MI dosage. The Langmuir equation model suited As(V), whereas As(III) related better to the Freundlich equation model due to different adsorption mechanisms. The predominant mechanism of As(V) adsorption onto MI is thought to be the electrostatic force between As(V) and MI, whereas As(III) in the solution bound to the adsorbed As(III) on the MI in a way consistent with van der Waals attraction. The removal rate of As(III) and As(V) has the highest adsorption efficiency in the pH 5–9 range. The adsorption of As(III) and As(V) was little affected by ionic strength, however the presence of H₄SiO₄₀ and PO₄³⁻ significantly reduced the arsenic adsorption capacity. Furthermore, the adsorption and regeneration efficiency of MI was maintained at around 100% for given adsorption–regeneration cycles.

A bivalent Cu(I,II) metal–organic framework (MOF) based on the 4,4′,4″-s-Triazine-2,4,6-triyl-tribenzoate linker was synthesized via a solvothermal method. The MOF possessed 43.8% of the Cu sites as Cu⁺ with a surface area of 1257 m² g⁻¹. The detailed spectroscopic analysis confirmed dimethylformamide (DMF) solvent as the reductant responsible for Cu⁺ sites in the synthesized MOF. The Cu⁺ sites were easily accessible and prone to oxidation in hot water or acidic gas environment. The MOF showed water-induced structural change, which could be partially recovered after soaking in DMF solvent. The synthesized MOF showed a high hydrogen sulfide (H₂S) uptake capacity of 4.3 mmol g^–1 at 298 K and an extremely low H₂S pressure of 0.0005 bar. The adsorption capacity was the highest among Cu-based MOFs with PCN-6-M being regenerable, which made it useful for deep desulfurization applications. The adsorbed H₂S was mineralized to sulfide, sulfur, and sulfates, mediated by the Cu⁺/Cu²⁺ redox cycle in the presence of adsorbed water and molecular oxygen. Thus, the study confirmed that DMF as a reductant is responsible for the origin of bivalency in PCN-6-M and possibly in other Cu-based MOFs reported in the literature. Also, the developed MOF could be a potential candidate for flue gas desulfurization and gas purification applications.

A ternary Mn–Zn–Fe oxide nanocomposite was fabricated by a one-step coprecipitation method for the remotion of H₂S and SO₂ gases at room temperature. The nanocomposite has ZnO, MnO₂, and ferrites with a surface area of 21.03 m² g⁻¹. The adsorbent was effective in mineralizing acidic sulfurous gases better in wet conditions. The material exhibited a maximum H₂S and SO₂ removal capacity of 1.31 and 0.49 mmol g⁻¹, respectively, in the optimized experimental conditions. The spectroscopic analyses confirmed the formation of sulfide, sulfur, and sulfite as the mineralized products of H₂S. Additionally, the nanocomposite could convert SO₂ to sulfate as the sole oxidation by-product. The oxidation of these toxic gases was driven by the dissolution and dissociation of gas molecules in surface adsorbed water, followed by the redox behaviour of transition metal ions in the presence of molecular oxygen and water. Thus, the study presented a potential nanocomposite adsorbent for deep desulfurization applications.