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Global temperature has risen >1 °C since the preindustrial era, resulting in well-documented adverse climate impacts including extreme weather (floods, droughts, storms, and heat waves), a rise in ...

Recent research in catalyst development for CO2 methanation has been focussing on the design of nanostructures with high porosity and better redox properties. Herein, nanostructured Ce0.8Zr0.2O2 mixed oxide support was prepared by a metal organic framework (MOF)-template approach and its properties were well compared with a similar catalyst prepared by a conventional coprecipitation (CP) method. The MOF-template approach resulted in the production of a nanoporous Ce0.8Zr0.2O2 support with improved redox properties compared to the coprecipitated Ce0.8Zr0.2O2. The prepared support was then decorated with Co3O4 nanoparticles and tested in CO2 methanation reaction. At 320 °C, 1.5 MPa and GHSV = 15,000 mL g˗1 h˗1, the Co/Ce0.8Zr0.2O2 catalyst prepared by MOF-template method achieved far better CO2 conversion (81.2%) and improved CH4 selectivity (99%) than the catalyst prepared by CP method (48.7% CO2 conversion and 97% CH4 selectivity). The long-time presence of the MOF-derived Co/Ce0.8Zr0.2O2 catalyst on the stream proved its resistance towards sintering, which may be ascribed to the fine dispersion of Co3O4 nanoparticles as well as their excellent integration in the network of nanoporous Ce0.8Zr0.2O2.

Herein, the catalytic performance of Fe/Nb/M (M = Mn, Co, Ni, and Cu) spinel ferrites prepared by a co-precipitation method for the high-temperature water-gas shift (HT-WGS) was investigated. Incorporation of Nb into the iron oxide lattice was found to moderately improve the catalytic activity. Conversely, the co-doping with Nb and transition metals (Mn, Co, Ni, and Cu) into the iron oxide matrix drastically enhanced the HT-WGS activity. The high lattice strain/disorder and facile Fe3+/Fe2+ redox cycle induced by the enhanced synergism in the Fe/Nb/M ternary catalysts serve as active sites to efficiently catalyze the WGS reaction. The results also indicate that the Nb acts as a textural promoter to improve the thermal stability of the active magnetite phase, while the transition metals act as structural promoters to enhance the WGS activity. The Fe/Nb/Ni exhibited the higher catalytic performance among the co-doped spinel ferrite catalysts. The high lattice strain/disorder, facile reduction of hematite to magnetite and highly facilitated surface Fe3+/Fe2+ redox pair by strong synergistic effect could be responsible for the better activity and stability of Fe/Nb/Ni in HT-WGS reaction. The characterizations of the spent Fe/Nb/Ni after 100 h of reaction revealed that the catalyst exhibited an excellent structural and surface stability during the reaction.

The capacity of an adsorbent to bind and remove dye from solution greatly depends on the type of functionalization present on the nanoparticles surface, and its interaction with the dye molecules. Within this study, nitrogenous silane nanoparticles were hydrothermally synthesized resulting in the formation of rapid and highly efficient adsorbents for concentrated mixed dyes. The amorphous silane nanoparticles exhibited a monolayer based mechanism of mixed dye adsorption with removal capacities between 416.67 and 714.29 mg/g of adsorbent. Dye removal was predominantly due to the electrostatic attraction between the positively charged silane nanoparticles (13.22–8.20 mV) and the negatively charged dye molecules (−54.23 mV). Addition of H. annuus extract during synthesis resulted in three times the surface area and 10 times increased pore volume compared to the positive control. XPS analysis showed that silane treatments had various nitrogen containing functionalities at their surface responsible for binding dye. The weak colloidal stability of silane particles (13.22–8.20 mV) was disrupted following dye binding, resulting in their rapid coagulation and flocculation which facilitated the separation of bound dye molecules from solution. The suitability for environmental applications using these treatments was supported by a bacterial viability assay showing >90% cell viability in treated dye supernatants.

Design and synthesis of efficient photocatalyst systems for a large volume of hydrogen (H2) evolution under solar light is still a great challenge. To obtain high photocatalytic activity, graphene-based semiconductor photocatalysts are gaining heightened attention in the field of green and sustainable fuel production due to their good electronic properties, high surface area and chemical stability. Herein, we demonstrate an efficient, novel and smart architecture of a graphene-based ZnIn2S4/g-C3N4 nanojunction by a simple hydrothermal process for H2 generation. In the present study, graphene (G) is chosen as the electron mediator and ZnIn2S4 (ZIS) and g-C3N4 (CN) are chosen as two different semiconductor photocatalysts to construct a smart architecture for the ternary photocatalytic system. Different characterization techniques such as XRD, TGA, FT-IR, SEM, TEM, HR-TEM, XPS, BET, and UV-vis DRS were employed to ensure the successful integration of graphene, ZnIn2S4, and g-C3N4 in the nanocomposite. As a result, high and efficient H2 evolution (477 μmol h−1 g−1) is attained for the graphene-based ZnIn2S4/g-C3N4 nanocomposite. Transient photocurrent experiments, ESR, PL, and time-resolved PL studies suggested that the intimate ternary nanojunction effectively promotes fast charge transfer and thereby enhances photocatalytic H2 evolution.

In this study, we developed a novel method of integrating the well-accepted cold vapor technique with gold nanostructured based quartz crystal microbalance (QCM) devices to selectively detect mercury ions (Hg2+). This method allows for the conversion of aqueous mercury ions into elemental mercury (Hg°) vapor form and thereon use the highly sensitive QCM based mercury vapor sensors to detect the evolved mercury. The method involves reducing mercury chloride (HgCl2) in contaminated water by mixing it with a 2% tin chloride (SnCl2) solution in order to evolve Hg° vapor from the liquid mixture. The selectivity and sensitivity performance of each gold nanostructure, namely, the control Au thin film (Au-ctrl), Au-nanospheres (Au-NS) and Au-nanourchins (Au-NU), towards mercury vapor was evaluated. It was found that Au-NS and Au-NU sensors displayed up to 79% and 243% higher response magnitudes than the Au-ctrl sensor for various concentrations of HgCl2, respectively. All three sensors exhibited repeatable sensing performance when reporting the concentrations from 5 sensing events involving 500 ppb HgCl2 solution with Au-ctrl, Au-NS and Au-NU having the coefficient of variance (CoV) values of ˜5.7, 2.9 and 3.8%, respectively. Moreover, the sensors were observed to operate in the linear region with the mercury ion concentration range calibrated and tested. Importantly, the sensors showed no cross-interference effects when tested toward Hg2+ ions with and without the presence of other metal ions such as lead, cadmium, manganese, iron, and zinc. The results indicate that the CV-QCM technique developed is feasible to be potentially used in real-world mercury monitoring applications.

The sustainable synthesis of high-quality graphene sheets is one of the hottest and most inspiring topics in the fields of science and engineering. While the graphene oxide (GO) chemical reduction ...

Synergistic composite metal oxides are proven to be impressive materials due to their multi-functionalities across various catalytic applications. In a composite metal oxide, the interfacial chemistry between the components could provide exceptional redox and catalytic properties. In the present manuscript, the fundamental focus is devoted to investigating the interactions between active metal oxides at their interfaces and the catalytic activities towards diesel soot and CO oxidation. A series of flower-like microspheres namely, CeO2, 10%Mn3O4/CeO2, 20%Mn3O4/CeO2, and 40%Mn3O4/CeO2 catalysts were synthesized, where the effect of different Mn3O4 loadings towards soot combustion and CO oxidation were investigated. The characteristic 50% conversion temperature (T50) of catalytic soot oxidation under loose and tight contact conditions for CeO2 microspheres are 502 and 484 °C, respectively. After the integration of Mn3O4 and CeO2, the T50 values were decreased with the lowest values observed for the 20%Mn3O4/CeO2 microspheres (381 and 350 °C). Similarly, 20%Mn3O4/CeO2 microspheres showed T50 value at 103 °C for CO oxidation when compared to pure CeO2 microspheres (216 °C) and Mn3O4 nanoparticles (356 °C). Activation energy values were decreased when the Mn3O4/CeO2 composite used in soot and CO oxidation. The high catalytic activity can be attributed to the strong synergistic interactions between CeO2 and Mn3O4, variable oxidation states, the amount of readily available surface redox active sites and oxygen vacancies. The possible interfacial interaction between CeO2 and Mn3O4 can be exploited to exhibit enhanced surface structural, and redox properties when compared to the pure counterparts. Post-catalytic oxidation analysis confirms the high stability of the Mn3O4/CeO2 composite. The present study points out the vital role of interfacial interactions in composite metal oxides for improving the surface and redox properties, which are important for the development of highly efficient soot and CO oxidation catalysts.

TiO2 nanorods-supported MnOx, FeOx, CrOx, and MnOx-FeOx-CrOx catalysts have been prepared by a deposition-precipitation method, with the aim of investigating the combination of ternary metal oxides effect on elemental mercury (Hg0) removal. The TiO2 nanorods-supported MnOx-FeOx-CrOx catalyst manifested the superior Hg0 removal efficiency (∼80-83%) at low temperatures (100–200 °C) in the presence of O2. The addition of NO promoted the Hg0 removal efficiency under the same reaction conditions. Further, SEM, HRTEM, XRD, BET surface area, and XPS characterization were carried out to explore the physicochemical properties of the catalysts. It was found that the integration of three active metal oxides contributed to the enrichment of active sites and the surface adsorbed oxygen species, thereby improving the catalytic activity. Additionally, both the large surface area and high crystallization of the obtained TiO2 nanorods resulted in uniform dispersion of the manganese-iron-chromium mixed metal oxide nanoparticles and a high activity. Further, XPS data of spent MnOx-FeOx-CrOx/TiO2 catalyst indicated that the presence of Mn4+, Cr6+, and Fe3+ could promote Hg0 oxidation due to the strong synergistic interaction between the TiO2 nanorods-incorporated MnOx, FeOx, and CrOx nanoparticles.

Complex organic molecules are of great importance to research and industrial chemistry and typically synthesized from smaller building blocks by multistep reactions. The ability to perform multiple (distinct) transformations in a single reactor would greatly reduce the number of manipulations required for chemical manufacturing, and hence the development of multifunctional catalysts for such one-pot reactions is highly desirable. Here we report the synthesis of a hierarchically porous framework, in which the macropores are selectively functionalized with a sulfated zirconia solid acid coating, while the mesopores are selectively functionalized with MgO solid base nanoparticles. Active site compartmentalization and substrate channelling protects base-catalysed triacylglyceride transesterification from poisoning by free fatty acid impurities (even at 50 mol%), and promotes the efficient two-step cascade deacetalization-Knoevenagel condensation of dimethyl acetals to cyanoates.

We report an enhancement in the efficiency of agitative liquid-phase exfoliation of stratified WS2 crystals under the influence of an electric field. We have been successfully able to increase the exfoliation efficiency of WS2 nanoflakes using a co-applied alternating electric field. Loss of centrosymmetry at the facial layers of WS2, together with the matching between the dispersive component of this material and solvent that weakens the van der Waals forces, augment the exfoliation process. However, this is not seen for MoS2 and graphene. The outcomes provide the base for future investigations on the influence of electric field for the exfoliation of layered structures.

Oxygen vacancies in inorganic semiconductors play an important role in reducing electron–hole recombination, which may have important implications in photocatalysis. Cuprous oxide (Cu2O), a visible light active p-type semiconductor, is a promising photocatalyst. However, the synthesis of photostable Cu2O enriched with oxygen defects remains a challenge. We report a simple method for the gram-scale synthesis of highly photostable Cu2O nanoparticles by the hydrolysis of a Cu(I)-triethylamine [Cu(I)–TEA] complex at low temperature. The oxygen vacancies in these Cu2O nanoparticles led to a significant increase in the lifetimes of photogenerated charge carriers upon excitation with visible light. This, in combination with a suitable energy band structure, allowed Cu2O nanoparticles to exhibit outstanding photoactivity in visible light through the generation of electron-mediated hydroxyl (OH˙) radicals. This study highlights the significance of oxygen defects in enhancing the photocatalytic performance of promising semiconductor photocatalysts.

In this work, various transition and rare earth metal ions (M3+; M = Mn3+, Fe3+, La3+, and Pr3+) doped CeO2 solid solutions were prepared by a simple sol–gel method for the degradation of an organic dye, Rhodamine B (RhB) as a model pollutant. The as-prepared samples were thoroughly studied by various characterization techniques to understand the surface and optical properties. The XRD results suggested formation of solid solutions, and TEM studies confirmed the nanosized nature of the ceria particles. The Raman and XPS results revealed that the doping of metal ions enhanced the formation of Ce3+ ions associated with the oxygen vacancies. The doping of M3+ ions in the CeO2 lattice strongly influenced the band gap tuning of undoped CeO2 (3.01 eV) from the UV to Visible region (i.e., 2.45–2.90 eV). Photoluminescence studies suggested that doping of M3+ cations suppresses the recombination rate of photogenerated electron–hole pairs. The photocatalytic activity results indicated that the doped CeO2 samples exhibit substantially enhanced photocatalytic performance for the degradation of RhB compared to undoped CeO2. The better catalytic activity of doped CeO2 samples could be attributed to the presence of defects (Ce3+ ions and oxygen vacancies), which play a prominent role as trapping centres for excited electrons and inhibit the recombination process. The scavengers tests confirmed that the generation of highly reactive hydroxyl (·OH) and super oxide (·O2−) radicals are actively involved in the photodegradation process. This work rendered a new concept for rational design and development of doped CeO2-based materials as better photocatalysts.

In the present work, nanowire morphologies of α-MnO2, cobalt monodoped α-MnO2, Cu and Co bidoped α-MnO2, and Ni and Co bidoped α-MnO2 samples were prepared by a facile hydrothermal synthesis. The structural, morphological, surface, and redox properties of all the as-prepared samples were investigated by various characterization techniques, namely, scanning electron microscopy (SEM), transmission and high resolution electron microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N2 sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H2-TPR), and oxygen-temperature-programmed desorption (O2-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO2 nanowires showed a remarkable improvement in soot oxidation performance, with its T50 (50% soot conversion) values of 279 and 431 °C under tight and loose contact conditions, respectively. The soot combust...

A novel one-step microwave irradiation method has been introduced to synthesize 3-mercaptopropionic acid capped CdTe QDs (Quantum dots). The synthesis process required no special conditions such as an inert nitrogen atmosphere but was carried out using TeO 2 (Tellurium oxide) as opposed to the Te powder, Na 2 TeO 3 or Al 2 TeO 3 usually used for the tellurium source. The characterization of the QDs revealed that they were 2–3 nm in size. The application of aqueous synthesis of capped CdTe QDs for latent fingerprinting was explored and fast turnaround times were achieved.

CeO2 nanoparticle-decorated ?-MnO2 nanotubes (NTs) were prepared and tested for elemental mercury (Hg0) vapor removal in simulated natural gas mixtures at ambient conditions. The composition which ...

In recent years, the development of artificial nanostructured enzymes has received enormous interest in nanobiotechnology due to their advantages over natural enzymes. In the present work, different amounts (5, 10, and 20 wt%) of Co3O4 nanoparticle decorated CeO2 hybrid flower-like microspheres (Co3O4@CeO2) have been investigated for peroxidase-like activity and it was found that 10 wt% of Co3O4@CeO2 exhibited excellent peroxidase-like activity for the catalytic oxidation of the 3,3′,5,5′-tetramethylbenzidine (TMB) substrate in the presence of H2O2. The formation of more Ce3+ ions associated with the oxygen vacancies and a strong synergistic interaction between CeO2 and Co3O4 may be responsible for the enhanced peroxidase-like activity. Based on their peroxidase activity, Co3O4@CeO2 hybrid microspheres were used for the colourimetric detection of glucose. It was found that Co3O4@CeO2 hybrid microspheres showed a substantial enhancement in the detection selectivity. The limit of detection (LOD) was also improved with a limit as low as 1.9 μM. Thus, we believe that Co3O4@CeO2 hybrid flower-like microspheres with high peroxidase-like activity can be exploited for biosensing applications.

In this investigation, Mn-doped CeO2(CM) catalysts were prepared by co-precipitation (CP), sol-gel (SG), and hydrothermal (HT) methods and characterized by XRD, ICP-OES, N2 adsorption–desorption, SEM, TEM-HREM, Raman, XPS, FT-IR, XPS and H2-TPR techniques, and evaluated for CO oxidation activity. The CM catalyst obtained by HT method showed superior CO oxidation performance at much lower temperature (T50 = ~355 K). The better performance of CM-HT catalyst is ascribed to its larger surface area, higher concentration of surface adsorbed oxygen, enhanced reducibility, and more oxygen vacancy sites. Further, it was found that the CM-HT catalyst is fully recyclable for over four runs while maintaining its high activity, which suggests that it is a better catalyst for CO oxidation at lower temperatures.

The construction of highly efficient inorganic mimetic enzymes (nanozymes) is much needed to replace natural enzymes due to their instability and high cost. Recently, nanoscale CeO2 has been attracting significant interest due to its unique properties such as facile redox behaviour (Ce4+ ↔ Ce3+) and surface defects. In the present work, various amounts of Fe3+-doped CeO2 nanorods (NRs) (with 3, 6, 9, and 12% Fe doping) were synthesized using a facile hydrothermal method and investigated for peroxidase-like activity and glucose detection. The peroxidase-like activity results revealed that 6 at% doping is the optimal Fe doping level to demonstrate superior catalytic performance over un-doped and Fe3+-doped CeO2 NRs. Steady state kinetic analysis also confirms that the 6% Fe3+-doped CeO2 (6Fe/CeO2) NRs exhibited excellent catalytic performance towards 3,3′,5,5′tetramethylbenzidine (TMB) oxidation with a Km and Vm of 0.176 mM and 8.6 × 10−8 M s−1, respectively, as compared to horseradish peroxidase (HRP) enzymes (0.434 mM and 10.0 × 10−8 M s−1). Typical colour reactions arising from the catalytic oxidation of the TMB substrate over 6Fe/CeO2 NRs with H2O2 have been utilized to establish a simple sensitive and selective colorimetric assay for the determination of glucose concentration in buffer, diluted fruit juices and foetal bovine serum samples. The superior catalytic performance of 6Fe/CeO2 NRs could be attributed to abundant surface defects, high surface area and pore volume, and preferential exposure of the highly reactive (110) planes.

Surface active sites such as oxygen vacancies, Ce3+ ions, and unsaturated coordinated sites on nano ceria (CeO2) are significant in catalytic oxidation reactions. The recent development in nanoengineered CeO2 made a pathway to extend its use in various catalytic applications. In this study, transition metals (Mn2+, Ni2+, and Co2+) doped CeO2 nanorods (NRs) were prepared by hydrothermal method and tested towards CO oxidation. Furthermore, the samples were characterized by various physicochemical techniques, namely, TEM and HR-TEM, SEM-EDX, XRD, ICP-OES, BET surface area, Raman spectroscopy, XPS, and H2-TPR. The results demonstrated that the incorporation of dopants greatly enhances the surface defective sites (Ce3+ ions and a high degree of surface roughness) and redox properties of CeO2 NRs and thereby improved catalytic activity. Especially, the Co–CeO2 NR catalyst exhibited better CO conversion (T50 ∼ 145 °C) when compared to pure CeO2 NR (T50 ∼ 312 °C).

A series of MnOx/CeO2 (Mn/Ce), MnOx/ZrO2 (Mn/Zr), and MnOx/Ce0.75Zr0.25O2 (Mn/CZ) catalysts prepared by an impregnation method were tested for their ability to catalyse the oxidation of Hg0 at relatively low temperature (423 K). Various characterization techniques, namely, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) were employed to understand the structural, surface, and redox properties of the prepared catalysts. Specific aspects of the catalysis of Hg0 oxidation that were investigated included the influence of MnOx loading (5, 15, and 25%) and the influence of HCl and O2. Among the catalysts tested, the 15Mn/CZ catalyst achieved the best Hg0 oxidation performance (~83% conversion of Hg0 to Hg2+) in the presence of HCl and O2. The higher activity of the 15Mn/CZ catalyst was most likely due to the presence of more oxygen vacancies, enhanced Mn4+/Mn4+ + Mn3+ + Mn2+ ratio and more surface adsorbed oxygen, which were proved by XRD, BET, Raman, and XPS. H2-TPR results also show that the strong interaction between the Ce0.75Zr0.25O2 support and MnOx improved the redox properties significantly as compared to pure CeO2 and ZrO2 supported MnOx catalysts.

Mercury pollution threatens the environment and human health across the globe. This neurotoxic substance is encountered in artisanal gold mining, coal combustion, oil and gas refining, waste incineration, chloralkali plant operation, metallurgy, and areas of agriculture in which mercury‐rich fungicides are used. Thousands of tonnes of mercury are emitted annually through these activities. With the Minamata Convention on Mercury entering force this year, increasing regulation of mercury pollution is imminent. It is therefore critical to provide inexpensive and scalable mercury sorbents. The research herein addresses this need by introducing low‐cost mercury sorbents made solely from sulfur and unsaturated cooking oils. A porous version of the polymer was prepared by simply synthesising the polymer in the presence of a sodium chloride porogen. The resulting material is a rubber that captures liquid mercury metal, mercury vapour, inorganic mercury bound to organic matter, and highly toxic alkylmercury compounds. Mercury removal from air, water and soil was demonstrated. Because sulfur is a by‐product of petroleum refining and spent cooking oils from the food industry are suitable starting materials, these mercury‐capturing polymers can be synthesised entirely from waste and supplied on multi‐kilogram scales. This study is therefore an advance in waste valorisation and environmental chemistry.