Exfoliated Ni-Al LDH 2D nanosheets for intermediate temperature CO2 capture

Kinetics, isotherm, mechanism, and recyclability of novel nano-sized Ce4+-doped Ni-Al layered double hydroxide for defluoridation of aqueous solutions

Excessive fluoride removal from aqueous solutions is of utmost importance as it has an adverse impact on human health. This study investigates the defluoridation efficiency of a novel nano-sized Ce+4-doped Ni/Al layered double hydroxide (Ni-Al-Ce LDH) for aqueous solutions. The synthesized Ni-Al-Ce LDH exhibited a well-defined nanoscale plate-like morphology and a high surface area with an average size of 11.51 nm, which contributed to its enhanced fluoride adsorption capacity. XRD, SEM, HRTEM, and BET studies confirmed these characteristics. XPS analysis confirmed the presence of Ce4+ ions within the Ni-Al LDH. The experimental results indicated that the process of defluoridation followed a pseudo-second-order model of kinetics, suggesting a chemisorption mechanism. The fluoride adsorption isotherms demonstrated well fits to the Freundlich, Langmuir, and Jovanovic models, indicating both monolayer and multilayer fluoride adsorption on the Ce-doped Ni-Al LDH. The maximum adsorption capacity was found to be 238.27 mg/g (Langmuir) and 130.73 mg/g (Jovanovic) at pH 6.0 and 25 °C. The proposed mechanisms for fluoride adsorption on the LDH include ion exchange, surface complexation, hydrogen bonding, and ligand exchange. The Ni-Al-Ce LDH nanomaterial exhibited good recyclability, maintaining 71% of the fluoride adsorption efficiency even after four consecutive cycles. This study highlights the significant role of Ce doping in improving the performance of Ni-Al LDH as a defluoridation adsorbent.

Controllable Doping of Mn into Ni0.075-xMnxAl0.025(OH)2(CO3)0.0125·yH2O for Efficient Adsorption of Fluoride Ions

Here, the structural, optical, and adsorptive behaviors of Ni_0.075-xMn_xAl_0.025(OH)₂(CO₃)_0.0125·yH₂O (Ni-Mn/Al) layered double hydroxides (LDHs) are investigated to capture fluoride from aqueous media. The 2D mesoporous plate-like Ni-Mn/Al LDHs are successfully prepared via a co-precipitation method. The molar ratio of divalent to trivalent cations is maintained at 3:1 and the pH at 10. The X-ray diffraction (XRD) results confirm that the samples consist of pure LDH phases with a basal spacing of 7.66 to 7.72 Å, corresponding to the (003) planes at 2θ of 11.47^o and the average crystallite sizes of 4.13 to 8.67 nm. The plate-like Mn-doped Ni-Al LDH consists of many superimposed nanosheets with a size of 9.99 nm. Energy-dispersive X-ray and X-ray photoelectron spectroscopies confirm the incorporation of Mn²⁺ into the Ni-Al LDH. UV-vis diffuse reflectance spectroscopy results indicate that incorporating Mn²⁺ into LDH enhances its interaction with light. The experimental data from the batch fluoride adsorption studies are subjected to kinetic models such as pseudo-first order and pseudo-second order. The kinetics of fluoride retention on Ni-Mn/Al LDH obey the pseudo-second-order model. The Temkin equation well describes the equilibrium adsorption of fluoride. The results from the thermodynamic studies also indicate that fluoride adsorption is exothermic and spontaneous.

Removal and recovery of phosphorus from secondary effluent using layered double hydroxide-biochar composites

Removal of phosphorus (P) from wastewater and its recovery as a fertilizer are solutions to both P pollution control and resource recycling for agriculture. In this study, various layered double hydroxide biochar composites (LDH/BCs), namely, Zn-Al-LDH/BC, Mg-Al-LDH/BC, and Mg-Fe-LDH/BC, were synthesized to remove P from secondary effluents and then applied as fertilizers. Batch experiments showed that LDH/BCs could adsorb P in fast kinetics, with adsorption capacities ranging 35.19-55.76 mg P/g. A dynamic experiment was performed under different column heights and flow rates, and the results fitted well with Thomas model (R² > 0.90). These LDH/BCs effectively removed P in the continuous mode, even when treating secondary effluents. Furthermore, when the used LDH/BCs applied as fertilizers, the adsorbed Mg-Al-LDH/BC and Mg-Fe-LDH/BC stimulated crop growth; however, Zn-Al-LDH/BC did not. These differences were attributed to not only the availability of P, but also the stimulation or inhibition of photosynthetic pigment synthesis in crops by adsorbents. Overall, we synthesized LDH/BCs, which effectively removed and recovered P from secondary effluents, and investigated the factors influencing the effects of LDH/BCs on crops. We suggest that both P availability and physiological influences of adsorbents on crops should be considered when using adsorbents as fertilizers.

Transition-Metal-Doped SiP2 Monolayer for Effective CO2 Capture: A Density Functional Theory Study

Two-dimensional materials have exhibited great potential in mitigating climate change through sensing and capturing carbon dioxide. The interaction of CO₂ on orthorhombic silicon diphosphide remains unexplored in spite of its interesting properties such as high carrier mobility, piezoelectricity, and mechanical stability. Here, using density functional theory, the adsorption of CO₂ on pristine and Ti-, V-, and Cr-doped monolayer SiP₂ is investigated. Doped systems exhibited significantly stronger adsorption (-0.268 to -0.396 eV) than pristine SiP₂ (-0.017 to -0.031 eV) and have the possibility of synthesis with low defect formation energies. Our results on adsorption energy, band structure, partial density of states, and charge transfer conclude that titanium- and vanadium-doped SiP₂ monolayers would be promising materials for CO₂ capture and removal.

LDH Nanocubes Synthesized with Zeolite Templates and Their High Performance as Adsorbents

In this work, the efficiency of the adsorptive removal of the organic cationic dye methylene blue (MB) from polluted water was examined using three materials: natural clay (zeolite), Zn-Fe layered double hydroxide (LDH), and zeolite/LDH composite. These materials were characterized via X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX) diffraction (XRF), low-temperature N2 adsorption, pore volume and average pore size distribution and field emission scanning electron microscopy (FE-SEM). The properties of the applied nanomaterials regarding the adsorption of MB were investigated by determining various experimental parameters, such as the contact time, initial dye concentration, and solution pH. In addition, the adsorption isotherm model was estimated using the Langmuir, Freundlich, and Langmuir-Freundlich isotherm models. The Langmuir model was the best-fitting for all applied nanomaterials. In addition, the kinetics were analyzed by using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models, and the pseudo-second-order model was an apparent fit for all three applied nanomaterials. The maximum Adsorption capacity toward MB obtained from the materials was in the order zeolite/LDH composite > zeolites > Zn-Fe LDH. Thus, the zeolite/LDH composite is an excellent adsorbent for the removal of MB from polluted water.

Understanding the Effect of Water on CO2 Adsorption

Carbon capture from large sources and ambient air is one of the most promising strategies to curb the deleterious effect of greenhouse gases. Among different technologies, CO₂ adsorption has drawn widespread attention mostly because of its low energy requirements. Considering that water vapor is a ubiquitous component in air and almost all CO₂-rich industrial gas streams, understanding its impact on CO₂ adsorption is of critical importance. Owing to the large diversity of adsorbents, water plays many different roles from a severe inhibitor of CO₂ adsorption to an excellent promoter. Water may also increase the rate of CO₂ capture or have the opposite effect. In the presence of amine-containing adsorbents, water is even necessary for their long-term stability. The current contribution is a comprehensive review of the effects of water whether in the gas feed or as adsorbent moisture on CO₂ adsorption. For convenience, we discuss the effect of water vapor on CO₂ adsorption over four broadly defined groups of materials separately, namely (i) physical adsorbents, including carbons, zeolites and MOFs, (ii) amine-functionalized adsorbents, and (iii) reactive adsorbents, including metal carbonates and oxides. For each category, the effects of humidity level on CO₂ uptake, selectivity, and adsorption kinetics under different operational conditions are discussed. Whenever possible, findings from different sources are compared, paying particular attention to both similarities and inconsistencies. For completeness, the effect of water on membrane CO₂ separation is also discussed, albeit briefly.

Unveiling the exceptional synergism-induced design of Co-Mg-Al layered triple hydroxides (LTHs) for boosting catalytic activity toward the green synthesis of indol-3-yl derivatives under mild conditions

The current study provides a novel insight into the role of synergism of the changes in Mg²⁺/ Al³⁺ in the best catalytic activity of indol-3-yl derivatives. A series of Co-Mg-Al layered triple hydroxides (LTHs) catalysts were produced by altering the Al³⁺/Mg²⁺ ratio with respect to Co²⁺. The physicochemical properties of LTHs were well characterized by ICP-AES, XRD, FTIR, FE-SEM, BET, Zeta-sizer, and VSM. The results show that the sample CMA4 (Co²⁺:Mg²⁺:Al³⁺ 2:4:4) is an exception to the physicochemical characteristics of the produced Co-Mg-Al LTHs, which is due to the synergism between the changes in Mg²⁺ and Al³⁺. To the best of our knowledge, this is the first study to report the synthesis of indol-3-yl derivatives from indole-3-carbaldehyde using Co-Mg-Al LTHs as highly efficient heterogeneous catalysts, which is an extremely appealing path. The selectivity of the synthesis was studied by condensing various nucleophiles through the one-pot method that established superior reactivity under mild conditions. Notably, the results show that the Co-Mg-Al LTHs system exhibited an extraordinarily catalytic activity, with the highest yield (98%) being obtained under the following optimal conditions: the concentration of Co-Mg-Al LTHs = 5 mol%, 30 min., water/ethanol as solvent. Furthermore, the reusable studies exhibited that the catalysts were found to be stable and reusable for up to six cycles without substantial loss of catalytic activity. Finally, a plausible reaction mechanism of the Co-Mg-Al LTHs system for indol-3-yl derivatives was put forward according to our comprehensive analysis. Our work illuminates a cheap and flexible strategy for the synthesis of indol-3-yl derivatives using Co-Mg-Al LTHs.

Carbon dioxide capture in biochar produced from pine sawdust and paper mill sludge: Effect of porous structure and surface chemistry

The CO₂ concentration in the atmosphere is increasing and threatening the earth's climate. Selective CO₂ capture at large point sources will help to reduce the CO₂ emissions to the atmosphere. Biochar with microporous structure could be a potential material to capture CO₂. The impact of feedstock type, pyrolysis temperature and steam activation of biochars were evaluated for CO₂ adsorption capacity. Pine sawdust biochars were produced at 550 °C, and steam activated for 45 min at the same temperature after completing the pyrolysis (PS550 and PSS550). Paper mill sludge biochars were produced at 300 and 600 °C (PMS300 and PMS600). The CO₂ adsorption capacity of biochars was tested at 25 °C using a volumetric sorption analyzer. Pine sawdust biochars showed significantly higher CO₂ adsorption capacity than paper mill sludge biochars due to high surface area and microporosity. Pine sawdust biochars were then evaluated for dynamic adsorption under representative post-combustion flue gas concentration conditions (15% CO₂, 85% N₂) using a breakthrough rig. Both materials showed selective CO₂ uptake over N₂ which is the major component along with CO₂ in flue gas. PSS550 had slightly higher CO₂ adsorption capacity (0.73 mmol g^^-1 vs 0.67 mmol g^^-1) and CO₂ over N₂ selectivity (26 vs 18) than PS550 possibly due to increase of microporosity, surface area, and oxygen containing basic functional groups through steam activation. Pine sawdust biochar is an environmentally friendly and low-cost material to capture CO₂.

Photocatalytic degradation of gemifloxacin antibiotic using Zn-Co-LDH@biochar nanocomposite

The aim of the present study was to investigate the photocatalytic performance of biochar (BC)-incorporated Zn-Co-layered double hydroxide (LDH) nanostructures in gemifloxacin (GMF) degradation as a model pharmaceutical pollutant. The as-prepared Zn-Co-LDH@BC showed high photocatalytic efficiency due to the enhanced separation of photo-generated charge carriers using cobalt hydroxide as well as inhibiting the agglomeration of LDH nanostructures by incorporation of BC. According to the results, 92.7% of GMF was degraded through photocatalysis in the presence of Zn-Co-LDH catalyst. The photocatalytic performance of BC-incorporated Zn-Co-LDH was highly dependent on the solute concentration and photocatalyst dosage. The addition of ethanol caused more inhibiting effect than that of benzoquinone (BQ), indicating the major role of ^•OH in decomposition of GMF compared to the negligible role of O₂^•-. A greater enhancement in the photocatalytic degradation of GMF was obtained when the photoreactor containing Zn-Co-LDH@BC nanostructures was oxygenated. Less than 10% drop in the removal efficiency of GMF was observed within five successive operational runs. The results of chemical oxygen demand (COD) analysis indicated the COD removal efficiency of about 80% within 200 min, indicating the acceptable mineralization of GMF. The reaction pathways were also proposed for the photocatalytic conversion of GMF under UV light irradiation.

2D nanostructures beyond graphene: preparation, biocompatibility and biodegradation behaviors

The research advances of the preparation, biocompatibility and biodegradation of 2D nanomaterials are introduced. The prospects and challenges of the biomedical applications of 2D nanomaterials are summarized.

Intercalation chemistry and thermal characteristics of layered double hydroxides possessing organic phosphonates and sulfonates

The distinct roles of organic sulfonates that enable delamination in water and formation of microporous structures via thermal activation are elucidated.

Hydroxides Ni(OH)2&Ce(OH)3 as a novel hole storage layer for enhanced photocatalytic hydrogen evolution

In this work, a novel photocatalyst Ni(OH)₂&Ce(OH)₃@P-CdS was synthesized successfully by phosphorization of CdS and in situ loading of Ni(OH)₂&Ce(OH)₃ on the surface of P-CdS.