Flexible Linker-Based Triazine-Functionalized 2D Covalent Organic Frameworks for Supercapacitor and Gas Sorption Applications.

Covalent organic frameworks (COFs) having a large surface area, porosity, and substantial amounts of heteroatom content are recognized as the ideal class of materials for energy storage and gas sorption applications. In this work, we have synthesized four different porous COF materials by the polycondensation of a heteroatom-rich flexible triazine-based trialdehyde linker, namely 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine (TPT-CHO), with four different triamine linkers. Triamine linkers were chosen based on differences in size, symmetry, planarity, and heteroatom content, leading to the synthesis of four different COF materials named IITR-COF-1, IITR-COF-2, IITR-COF-3, and IITR-COF-4. IITR-COF-1, synthesized within 24 h from the most planar and largest amine monomer, exhibited the largest Brunauer-Emmett-Teller (BET) surface area of 2830 m2 g-1, superior crystallinity, and remarkable reproducibility compared to the other COFs. All of the synthesized COFs were explored for energy and gas storage applications. It is shown that the surface area and redox-active triazene rings in the materials have a profound effect on energy and gas storage enhancement. In a three-electrode setup, IITR-COF-1 achieved an electrochemical stability potential window (ESPW) of 2.0 V, demonstrating a high specific capacitance of 182.6 F g-1 with energy and power densities of 101.5 Wh kg-1 and 298.3 W kg-1, respectively, at a current density of 0.3 A g-1 in 0.5 M K2SO4 (aq) with long-term durability. The symmetric supercapacitor of IITR-COF-1//IITR-COF-1 exhibited a notable specific capacitance of 30.5 F g-1 and an energy density of 17.0 Wh kg-1 at a current density of 0.12 A g-1. At the same time, it demonstrated 111.3% retention of its initial specific capacitance after 10k charge-discharge cycles. Moreover, it exhibited exceptional CO2 capture capacity of 25.90 and 10.10 wt % at 273 and 298 K, respectively, with 2.1 wt % of H2 storage capacity at 77 K and 1 bar.

Graft onto approaches for nanocellulose-based advanced functional materials.

The resurgence of cellulose as nano-dimensional 'nanocellulose' has unlocked a sustainable bioeconomy for the development of advanced functional biomaterials. Bestowed with multifunctional attributes, such as renewability and abundance of its source, biodegradability, biocompatibility, superior mechanical, optical, and rheological properties, tunable self-assembly and surface chemistry, nanocellulose presents exclusive opportunities for a wide range of novel applications. However, to alleviate its intrinsic hydrophilicity-related constraints surface functionalization is inevitably needed to foster various targeted applications. The abundant surface hydroxyl groups on nanocellulose offer opportunities for grafting small molecules or macromolecular entities using either a 'graft onto' or 'graft from' approach, resulting in materials with distinctive functionalities. Most of the reviews published to date extensively discussed 'graft from' modification approaches, however 'graft onto' approaches are not well discussed. Hence, this review aims to provide a comprehensive summary of 'graft onto' approaches. Furthermore, insight into some of the recently emerging applications of this grafted nanocellulose including advanced nanocomposite formulation, stimuli-responsive materials, bioimaging, sensing, biomedicine, packaging, and wastewater treatment has also been reviewed.

A sustainable management of polycyclic aromatic hydrocarbons to synthesize microporous organic polymers for adsorptive desulphurization of fuels.

A sustainable management of carcinogenic polycyclic aromatic hydrocarbons (PAHs) to synthesize a series of high surface area (SABET of 563-1553 m2 g-1) microporous polymeric adsorbents is reported. The products with high yield (>90%) were obtained within only 30 min at a low temperature of 50 °C using a microwave-assisted approach with 400 W microwave power followed by 30 min of ageing by raising the temperature to 80 °C. The synthesized adsorbents are used for removing another category of carcinogenic pollutants i.e., polycyclic aromatic sulphur heterocycles (PASHs) from model and real fuels. Adsorptive desulphurization experiment in batch mode could reduce the sulphur from high concentrated model (100 ppm) and real (102 ppm) fuels to 8 ppm and 45 ppm respectively. Similarly, desulphurization of model and real fuels with ultralow sulphur concentrations of 10 and 9 ppm, respectively, reduced the final concentration of sulphur to 0.2 and 3 ppm, respectively. Adsorption isotherms, kinetics, and thermodynamic studies have been conducted using batch mode experiments. Adsorptive desulphurization using fixed bed column studies show the breakthrough capacities of 18.6 and 8.2 mgS g-1, for the same high concentrated model and real fuels, respectively. The breakthrough capacities of 1.1 and 0.6 mgS g-1 are estimated for the ultralow sulphur model and real fuels, respectively. The adsorption mechanism, based on the spectroscopic analysis (FTIR and XPS) demonstrates the role of π-π interactions between the adsorbate and adsorbent. The adsorptive desulphurization studies of model and real fuels from batch to fixed bed column mode would offer an in-depth understanding to demonstrate the lab-scale findings for industrial applications. Thus, the present sustainable strategy could manage two classes of carcinogenic petrochemical pollutants, PAHs and PASHs, simultaneously.

Machine learning implemented exploration of the adsorption mechanism of carbon dioxide onto porous carbons.

Adsorption of CO2 on porous carbons has been identified as one of the promising methods for carbon capture, which is essential for meeting the sustainable developmental goal (SDG) with respect to climate action, i.e., SDG 13. This research implemented six supervised machine learning (ML) models (gradient boosting decision tree (GBDT), extreme gradient boosting (XGB), light boost gradient machine (LBGM), random forest (RF), categorical boosting (Catboost), and adaptive boosting (Adaboost)) to understand and predict the CO2 adsorption mechanism and adsorption uptake, respectively. The results recommended that the GBDT outperformed the remaining five ML models for CO2 adsorption. However, XGB, LBGM, RF, and Catboost also represented the prediction in the acceptable range. The GBDT model indicated the accurate prediction of CO2 uptake onto the porous carbons considering adsorbent properties and adsorption conditions as model input parameters. Next, two-factor partial dependence plots revealed a lucid explanation of how the combinations of two input features affect the model prediction. Furthermore, SHapley Additive exPlainations (SHAP), a novel explication approach based on ML models, were employed to understand and elucidate the CO2 adsorption and model prediction. The SHAP explanations, implemented on the GBDT model, revealed the rigorous relationships among the input features and output variables based on the GBDT prediction. Additionally, SHAP provided clear-cut feature importance analysis and individual feature impact on the prediction. SHAP also explained two instances of CO2 adsorption. Along with the data-driven insightful explanation of CO2 adsorption onto porous carbons, this study also provides a promising method to predict the clear-cut performance of porous carbons for CO2 adsorption without performing any experiments and open new avenues for researchers to implement this study in the field of adsorption because a lot of data is being generated.

Photo- and Electrocatalytic Reduction of CO2 over Metal-Organic Frameworks and Their Derived Oxides: A Correlation of the Reaction Mechanism with the Electronic Structure.

A Ce/Ti-based bimetallic 2-aminoterephthalate metal-organic framework (MOF) was synthesized and evaluated for photocatalytic reduction of CO2 in comparison with an isoreticular pristine monometallic Ce-terephthalate MOF. Owing to highly selective CO2 adsorption capability, optimized band gaps, higher flux of photogenerated electron-hole pairs, and a lower rate of recombination, this material exhibited better photocatalytic reduction of CO2 and lower hydrogen evolution compared to Ce-terephthalate. Thorough probing of the surface and electronic structure inferred that the reducibility of Ce4+ to Ce3+ was due to the introduction of an amine functional group into the linker, and low-lying Ti(3d) orbitals in Ce/Ti-2-aminoterephthalate facilitated the photoreduction reaction. Both the MOFs were calcined to their respective oxides of Ce1-xTixO2 and CeO2, and the electrocatalytic reduction of CO2 was performed over the oxidic materials. In contrast to the photocatalytic reaction mechanism, the lattice substitution of Ti in the CeO2 fluorite cubic structure showed a better hydrogen evolution reaction and consequently, poorer electroreduction of CO2 compared to pristine CeO2. Density functional theory calculations of the competitive hydrogen evolution reaction on the MOF and the oxide surfaces corroborated the experimental findings.

Plant-based nanocellulose: A review of routine and recent preparation methods with current progress in its applications as rheology modifier and 3D bioprinting.

"Nanocellulose" have captivated the topical sphere of sturdily escalating market for sustainable materials. The review focuses on the comprehensive understanding of the distinct surface chemistry and functionalities pertaining to the renovation of macro-cellulose at nanodimensional scale to provide an intuition of their processing-structure-function prospective. The abundant availability, cost effectiveness and diverse properties associated with plant-based resources have great economical perspective for developing sustainable cellulose nanomaterials. Hence, emphasis has been given on nanocellulose types obtained from plant-based sources. An overarching goal is to provide the recent advancement in the preparation routes of nanocellulose. Considering the excellent shear thinning/thixotropic/gel-like behavior, the review provids an assemblage of publications specifically dealing with its application as rheology modifier with emphasis on its use as bioink for 3D bioprinting for various biomedical applications. Altogether, this review has been oriented in a way to collocate a collective data starting from the historical perspective of cellulose discovery to modern cellulosic chemistry and its renovation as nanocellulose with recent technological hype for broad spanning applications.

Tuning the morphology of CeO2 nanostructures using a template-free solvothermal process and their oxygen reduction reaction activity.

In fuel cells, the oxygen reduction reaction (ORR) at the cathode plays a crucial role in their performance. High cost, low abundance, catalyst poisoning, and poor durability of the pioneering ORR catalyst Pt make it less desirable for commercial fuel cells. Herein, we demonstrate a greener process to synthesize CeO2 nanostructures by varying reaction parameters in a single-step solvothermal route and provide a detailed mechanism for the formation of CeO2 nanostructures with different shapes. The shape and size of the CeO2 nanostructures such as hollow/solid spheres, triangular flakes, nanotubes, and flower-like structures result in a strong effect on their ORR activity. A normalized effect of effective surface area and oxygen vacancies in CeO2 nanostructures is found to govern the ORR activity order. Among the CeO2 nanostructures, hollow spheres exhibit the best ORR activity with a four-electron reduction pathway. Moreover, they show comparable ORR activity and outstanding stability as well as methanol fuel tolerance and are a substitute for Pt/C.

Correction: Citrate combustion synthesized Al-doped CaCu3Ti4O12 quadruple perovskite: synthesis, characterization and multifunctional properties.

Correction for 'Citrate combustion synthesized Al-doped CaCu3Ti4O12 quadruple perovskite: synthesis, characterization and multifunctional properties' by Kamalesh Pal et al., Phys. Chem. Chem. Phys., 2020, 22, 3499-3511, DOI: 10.1039/C9CP05005A.

Enhancing photocatalytic degradation of quinoline by ZnO:TiO2 mixed oxide: Optimization of operating parameters and mechanistic study.

This study focuses on the photocatalytic degradation of quinoline, a recalcitrant heterocyclic nitrogenous aromatic organic compound, using the mixed oxide ZnO-TiO2 photo-catalyst. Photo-catalysts were synthesized by the solid-state reaction method at different calcination temperatures of 400 °C, 600 °C, and 800 °C. Different analytical methods, including Field emission scanning electron microscope, Brunauer-Emmett-Teller surface area, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy analysis were used for the catalyst characterization. The highest pore surface area of 57.9 m2g-1 was obtained for the photo-catalyst calcined at 400 °C. The effects of calcination temperature, solution pH, initial concentration, catalyst dose as well as irradiation time were studied. At the optimum condition, i.e., calcination temperature of 400 °C, pH ≈8 and catalyst dose of 2.5 gL-1, maximum quinoline degradation and total organic carbon (TOC) removal efficiency of ≈92% and ≈78% were obtained after 240 min for initial quinoline amount of 50 mgL-1. The 1st, 2nd, and nth-order kinetic models were applied to analyze the quinoline degradation rate. The photocatalytic mechanism was studied by drawing energy level diagram with the help of the band-gap structures of the ZnO and TiO2, potential of the free radicals like OH and O2 and HOMO-LUMO energy gap of the quinoline molecule. The proposed pathways of quinoline mineralization were suggested on the basis of the identified intermediates by the gas chromatograph-mass spectrometer analysis and scavenger study.

Citrate combustion synthesized Al-doped CaCu3Ti4O12 quadruple perovskite: synthesis, characterization and multifunctional properties.

The facile synthesis of the Al-doped CaCu3Ti4O12 quadruple perovskite, a well-known and vastly studied material for various technological applications, using the modified citrate combustion route along with structural, microstructural, and X-ray photoelectron spectroscopic (XPS) characterization and magnetic, dielectric and electrical properties has been investigated and reported here. The possible applications of the material as a Schottky barrier diode (SBD) in optoelectronic devices and as a catalyst in methanol steam reforming (MSR) reaction for hydrogen generation, hitherto unreported in the open literature, have also been explored. The compound is crystallized in the cubic body centered Im3[combining macron] space group and the particle size is found to be in nanodimension with rather narrow size distribution. The enhanced resistivity could be attributed to the grain boundary effect, and consequently, it exhibits better performance as a SBD compared to the undoped sample. Desired cationic composition with expected valence states within the probe range is confirmed by XPS analysis. A better catalytic activity towards MSR is noticed for the Al-doped CaCu3Ti4O12 compared to the undoped composition. These new findings, namely MSR activity and applicability in the Schottky device, have highlighted further the multifunctional nature of the material in energy related issues and would thus be of interest to the materials community searching for functional materials.

A multifunctional triazine-based nanoporous polymer as a versatile organocatalyst for CO2 utilization and C-C bond formation.

A triazine-based nanoporous multifunctional polymer with a SABET of 304 m2 g-1 has shown versatile catalytic activity in the conversion of CO2 to cyclic carbonates at 4 bar with almost 100% yield and selectivity, and in the conversion of CO2 to methanol and methane electrochemically. Additionally, it also catalyzes C-C bond formation via the Knoevenagel reaction.

Nitrogen Amelioration-Driven Carbon Dioxide Capture by Nanoporous Polytriazine.

Nitrogen-enriched nanoporous polytriazines (NENPs) have been synthesized by ultrafast microwave-assisted condensation of melamine and cyanuric chloride. The experimental conditions have been optimized to tune the textural properties by synthesizing materials at different times, temperatures, microwave powers, and solvent contents. The maximum specific surface area (SABET) of 840 m2 g-1 was estimated in the sample (NENP-1) synthesized at 140 °C with a microwave power of 400 W and reaction time of 30 min. One of the major objectives of achieving a large nitrogen content as high as 52 wt % in the framework was realized. As predicted, the nitrogen amelioration has benefitted the application by capturing a very good amount of CO2 of 22.9 wt % at 273 K and 1 bar. Moreover, the CO2 storage capacity per unit specific surface area (per m2 g-1) is highest among the reported nanoporous organic frameworks. The interaction of the CO2 molecules with the polytriazine framework was theoretically investigated by using density functional theory. The experimental CO2 capture capacity was validated from the outcome of the theoretical calculations. The superior CO2 capture capability along with the theoretical investigation not only makes the nanoporous NENPs superior adsorbents for the energy and environmental applications but also provides a significant insight into the fundamental understanding of the interaction of CO2 molecules with the amine functionalities of the nanoporous frameworks.

Cyclophosphazene-Based Hybrid Nanoporous Materials as Superior Metal-Free Adsorbents for Gas Sorption Applications.

Cyclophosphazene-based inorganic-organic hybrid nanoporous materials (CHNMs) have been synthesized by a facile solvothermal method. The condensation of pyrrole with the reaction product of phosphonitrilic chloride trimer and 4-hydroxybenzaldehyde resulted in the formation of high-surface-area CHNMs. The maximum specific surface area (SABET) of 1328 m2 g-1 with hierarchical pore structures having micropores centered at 1.18 nm and mesopores in the range of 2.6-3.6 nm was estimated from the N2 sorption analysis. Observation of high SABET could be attributed to the synergy effect exerted by the cyclophosphazene moiety owing to its three-dimensional paddle wheel structure. The metal-free adsorbent exhibited a high and reversible CO2 uptake of 22.8 wt % at 273 K and 1 bar. The performance is on the higher side among the reported metal-free inorganic-organic hybrid nanoporous adsorbents. Moreover, the high H2 uptake of 2.02 wt % at 77 K and 1 bar is an added advantage. The superior performance of the adsorbents for the gas sorption applications could be attributed to the combined effect of high SABET and hierarchical pore structure, which has made CHNMs good candidates for energy and environmental applications.

Mixed titanium, silicon, and aluminum oxide nanostructures as novel adsorbent for removal of rhodamine 6G and methylene blue as cationic dyes from aqueous solution.

Mixed oxide nanoparticles containing Ti, Si, and Al of 8-15 nm size range were synthesized using a combined sol-gel - hydrothermal method. Effects of composition on the structure, morphology, and optical properties of the nanoparticles were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microRaman spectroscopy, and diffuse reflectance spectroscopy (DRS). Dye removal abilities of the nanoparticles from aqueous solutions were tested for different cationic dyes. While all the mixed oxide nanoparticles revealed high and fast adsorption of cationic dyes, the particles containing Ti and Si turned out to be the best. The adsorption kinetics and equilibrium adsorption behavior of the adsorbate - adsorbent systems could be well described by pseudo-second-order kinetics and Langmuir isotherm model, respectively. Estimated thermodynamic parameters revealed the adsorption process is spontaneous, driven mainly by the electrostatic force between the cationic dye molecules and negative charge at nanoparticle surface. Highest dye adsorption capacity (162.96 mg MB/g) of the mixed oxide nanostructures containing Ti and Si is associated to their high specific surface area, and the presence of surface Si-O(δ-) groups, in addition to the hydroxyl groups of amorphous titania. Mixed oxide nanoparticles containing 75% Ti and 25% Si seen to be the most efficient adsorbents for removing cationic dye molecules from wastewater.

Iron phthalocyanine modified mesoporous titania nanoparticles for photocatalytic activity and CO2 capture applications.

An iron(II)phthalocyanine (Fepc) modified mesoporous titania (Fepc-TiO2) nanocatalyst with a specific surface area of 215 m(2) g(-1) has been synthesized by a hydrothermal method. Fepc-TiO2 degrades one of the highly toxic chemical warfare agents, sulfur mustard (SM), photocatalytically under sunlight with an exposure time of as low as 70 min. Furthermore, the mesoporous Fepc-TiO2 also captured 2.1 mmol g(-1) of CO2 at 273 K and 1 atm.

ZnO-modified cellulose fiber sheets for antibody immobilization.

Cellulose fiber sheets impregnated with saccharide capped-ZnO nanoparticles were used as bioactive materials for antibody immobilization. First, ZnO nanoparticles were synthesized in the presence of glucose (monosaccharide), sucrose (disaccharide) as well as alginic acid and starch (polysaccharides). The pine cellulose fibers were then modified by the obtained saccharide capped nanoparticles and further incorporated into the sheets. The presence of ZnO significantly improved the immobilization of the antibodies on the surface of the sheets. After rewetting the alginic acid-ZnO modified sheets with saline solution, the retention of antibodies was about 95%. A high degree of the immobilization of biomolecules is an important feature for possible fabrications of bioactive- or biosensing-papers and we successfully tested the sheets on the detection of blood types using (A, B, and D blood antibodies). The ZnO nanoparticles affected also the other properties of the sheets. The ZnO-modified fiber sheets showed higher values of tensile index (strength), smoothness and opacity, while the value of porosity was substantially lower than that of the unmodified sheet. The presence of ZnO nanoparticles provided also the antimicrobial activity to the sheets. They showed a strong activity against bacteria (Escherichia coli and Staphylococcus aureus) and strong resistance to the attack of cellulase producing fungus Gloeophyllum trabeum.

Porous covalent electron-rich organonitridic frameworks as highly selective sorbents for methane and carbon dioxide.

Carbon dioxide capture from point sources like coal-fired power plants is considered to be a solution for stabilizing the CO(2) level in the atmosphere to avoid global warming. Methane is an important energy source that is often highly diluted by nitrogen in natural gas. For the separation of CO(2) and CH(4) from N(2) in flue gas and natural gas, respectively, sorbents with high and reversible gas uptake, high gas selectivity, good chemical and thermal stability, and low cost are desired. Here we report the synthesis and CO(2), CH(4), and N(2) adsorption properties of hierarchically porous electron-rich covalent organonitridic frameworks (PECONFs). These were prepared by simple condensation reactions between inexpensive, commercially available nitridic and electron-rich aromatic building units. The PECONF materials exhibit high and reversible CO(2) and CH(4) uptake and exceptional selectivities of these gases over N(2). The materials do not oxidize in air up to temperature of 400 °C.

Synthesis of coesite nanocrystals from ethane bridged periodic mesoporous organosilica at low temperature and extreme pressure.

Coesite nanocrystals have been synthesized from periodic mesoporous organosilica (PMO) with (CH(2))(2) bridges heated at 300 °C for 150 min and 12 GPa. The crystals are not sintered, single crystalline, and have diameters of ca. 100-300 nm. Below 300 °C, an amorphous non-porous organosilica glass was obtained. Heating above 300 °C at 12 GPa results in the rapid crystal growth and micron size coesite crystals were formed.

Catalyst-free synthesis of transparent, mesoporous diamond monoliths from periodic mesoporous carbon CMK-8.

We report on the synthesis of optically transparent, mesoporous, monolithic diamond from periodic mesoporous carbon CMK-8 at a pressure of 21 GPa. The phase transformation is already complete at a mild synthesis temperature of 1,300 degrees C without the need of a catalyst. Surprisingly, the diamond is obtained as a mesoporous material despite the extreme pressure. X-ray diffraction, SEM, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, and Z-contrast experiments suggest that the mesoporous diamond is composed of interconnected diamond nanocrystals having diameters around 5-10 nm. The Brunauer Emmett Teller surface area was determined to be 33 m2 g(-1) according Kr sorption data. The mesostructure is diminished yet still detectable when the diamond is produced from CMK-8 at 1,600 degrees C and 21 GPa. The temperature dependence of the porosity indicates that the mesoporous diamond exists metastable and withstands transformation into a dense form at a significant rate due to its high kinetic inertness at the mild synthesis temperature. The findings point toward ultrahard porous materials with potential as mechanically highly stable membranes.