Insight into Organic Pollutant Adsorption Characteristics on a g-C3N4 Surface by Attenuated Total Reflection Spectroscopy and Molecular Dynamics Simulation

Exploring the synergistic effect of MXene@ZIF-8 hybrid composites for water treatment

Due to their exceptional physical and chemical properties, MXenes have been the focus of growing research attention for their potential to effectively eliminate a wide range of pollutants from the aquatic environment. However, disadvantages such as limited adsorption capacity due to low specific surface area and undeveloped porosity have led to challenges in using these materials. In this work, we use a well-known MXene, Ti3C2Tx, by decorating zeolitic imidazole frameworks (ZIF-8) between MXene layers (MX@ZIF) to remove methyl orange (MO) and ciprofloxacin (CIP), as well as, the effect of -O and -OH terminal groups on adsorption efficiency of MX@ZIF substrate is investigated. Our findings from molecular dynamics simulations showed that the MXO@ZIF and MXOH@ZIF systems have stronger electrostatic interactions than the MX@ZIF system due to the formation of hydrogen bonds between the -O, -OH terminal groups from the substrates and heteroatoms of pollutant molecules. Moreover, the van der Waals energy values in the MXOH@ZIF-CIP and MXOH@ZIF-MO systems are - 253.454 and - 201.660 kJ/mol, respectively, demonstrating the effective adsorption and removal of contaminants by designed substrates. The MD results show that the van der Waals interaction has a greater contribution than the electrostatic interaction in studied systems. Also, the number of contacts of pollutant molecules with the substrate increases with time, and the highest number of contacts belongs to the MXOH@ZIF-CIP and MXOH@ZIF-MO complexes, demonstrating that this substrate has a greater tendency to adsorb pollutants. Furthermore, the results of AIM calculations confirm the presence of non-covalent interactions between pollutant molecules and studied substrates. This study shows that MXOH/ZIF can be considered a promising high-performance adsorbent for removing organic dyes and antibiotics.

Molecular simulation-based insights into dye pollutant adsorption: A perspective review

Growing concerns about environmental pollution have highlighted the need for efficient and sustainable methods to remove dye contamination from various ecosystems. In this context, computational methods such as molecular dynamics (MD), Monte Carlo (MC) simulations, quantum mechanics (QM) calculations, and machine learning (ML) methods are powerful tools used to study and predict the adsorption processes of dyes on various adsorbents. These methods provide detailed insights into the molecular interactions and mechanisms involved, which can be crucial for designing efficient adsorption systems. MD simulations, detailing molecular arrangements, predict dyes' adsorption behaviour and interaction energies with adsorbents. They simulate the entire adsorption process, including surface diffusion, solvent layer penetration, and physisorption. QM calculations, especially density functional theory (DFT), determine molecular structures and reactivity descriptors, aiding in understanding adsorption mechanisms. They identify stable adsorption configurations and interactions like hydrogen bonding and electrostatic forces. MC simulations predict equilibrium properties and adsorption energies by sampling molecular configurations. ML methods have proven highly effective in predicting and optimizing dye adsorption processes. These models offer significant advantages over traditional methods, including higher accuracy and the ability to handle complex datasets. These methods optimize adsorption conditions, clarify adsorbent functionalization roles, and predict dye removal efficiency under various conditions. This research explores MD, MC, QM, and ML approaches to connect molecular interactions with macroscopic adsorption phenomena. Probing these techniques provides insights into the dynamics and energetics of dye pollutants on adsorption surfaces. The findings will aid in developing and optimizing new materials for dye removal. This review has significant implications for environmental remediation, offering a comprehensive understanding of adsorption at various scales. Merging microscopic data with macroscopic observations enhances knowledge of dye pollutant adsorption, laying the groundwork for efficient, sustainable removal technologies. Addressing the growing challenges of ecosystem protection, this study contributes to a cleaner, more sustainable future.

Molecular Simulation Studies of Pharmaceutical Pollutant Removal (Rosuvastatin and Simvastatin) Using Novel Modified-MOF Nanostructures (UIO-66, UIO-66/Chitosan, and UIO-66/Oxidized Chitosan)

The ubiquitous presence of pharmaceutical pollutants in the environment significantly threatens human health and aquatic ecosystems. Conventional wastewater treatment processes often fall short of effectively removing these emerging contaminants. Therefore, the development of high-performance adsorbents is crucial for environmental remediation. This research utilizes molecular simulation to explore the potential of novel modified metal-organic frameworks (MOFs) in pharmaceutical pollutant removal, paving the way for the design of efficient wastewater treatment strategies. Utilizing UIO-66, a robust MOF, as the base material, we developed UIO-66 functionalized with chitosan (CHI) and oxidized chitosan (OCHI). These modified MOFs' physical and chemical properties were first investigated through various characterization techniques. Subsequently, molecular dynamics simulation (MDS) and Monte Carlo simulation (MCS) were employed to elucidate the adsorption mechanisms of rosuvastatin (ROSU) and simvastatin (SIMV), two prevalent pharmaceutical pollutants, onto these nanostructures. MCS calculations demonstrated a significant enhancement in the adsorption energy by incorporating CHI and OCHI into UIO-66. This increased ROSU from -14,522 to -16,459 kcal/mol and SIMV from -17,652 to -21,207 kcal/mol. Moreover, MDS reveals ROSU rejection rates in neat UIO-66 to be at 40%, rising to 60 and 70% with CHI and OCHI. Accumulation rates increase from 4 Å in UIO-66 to 6 and 9 Å in UIO-CHI and UIO-OCHI. Concentration analysis shows SIMV rejection surges from 50 to 90%, with accumulation rates increasing from 6 to 11 Å with CHI and OCHI in UIO-66. Functionalizing UIO-66 with CHI and OCHI significantly enhanced the adsorption capacity and selectivity for ROSU and SIMV. Abundant hydroxyl and amino groups facilitated strong interactions, improving performance over that of unmodified UIO-66. Surface functionalization plays a vital role in customizing the MOFs for pharmaceutical pollutant removal. These insights guide next-gen adsorbent development, offering high efficiency and selectivity for wastewater treatment.

Flexible Synthesis of Bio-Hydroxyapatite/Chitosan Hydrogel Beads for Highly Efficient Orange G Dye Removal: Batch and Recirculating Fixed-Bed Column Study

The use of fish waste as a source material for the development of functional beads has significant potential applications in the fields of materials science and environmental sustainability. In this study, a biomaterial bead of chitosan was cross-linked with bio-hydroxyapatite (Bio-Hap/Cs) through the encapsulation process to create a stable and durable material. The beads are characterized using scanning electron microscopy combined with energy dispersive X-ray spectrometry, Fourier transform infrared spectroscopy, and X-ray diffraction techniques. The adsorption efficiency of Bio-Hap/Cs hydrogel beads was evaluated by using Orange G (OG) dye in both batch and recirculating column systems, and the effect of various parameters on the adsorption capacity was investigated. In the batch study, it was found that OG removal increased with an increasing pH and adsorbent dose. However, in the recirculating column system, a higher bed height and lower flow rate led to increased removal of the OG dye. The kinetic study indicated that the pseudo-second-order model provided a good description of OG adsorption onto Bio-Hap/Cs beads in both batch and recirculating processes, with a high coefficient correlation. The maximum adsorbed amounts are found to be 19.944 mg g-1 and 9.472 mg g-1 in batch and recirculating processes, respectively. Therefore, Bio-Hap/Cs hydrogel beads have demonstrated an effective and reusable material for OG dye remediation from aqueous solutions using recirculating adsorption processes.

Facile synthesis of S, N-co-doped carbon dots for bio-imaging, Fe3+ detection and DFT calculation

Turning waste into wealth, herein, two highly fluorescent N and S co-doped carbon dots (N, S-CDs-A and N, S-CDs-B) were synthesized by the hydrothermal reaction of contaminant reactive red 2 (RR2) and L-cysteine or L-methionine, respectively. The detailed morphology and structure of N, S-CDs were characterized by XRD, Raman spectrum, FTIR spectra, TEM, HRTEM, AFM and XPS. The maximum fluorescent of N, S-CDs-A and N, S-CDs-B are 565 and 615 nm under different excitation wavelengths with moderate fluorescence intensity of 14.0 % and 6.3 %, respectively. The microstructure models of N, S-CDs-A and N, S-CDs-B, which were induced by FT-IR, XPS and element analysis, had been applied in DFT calculation. The result indicated that the doping of S and N is beneficial to obtain the red-shift of fluorescent spectra. Both N, S-CDs-A and N, S-CDs-B showed highly sensitive and selective to Fe3+. N, S-CDs-A can also detect Al3+ ion with high sensitivity and selectivity. Finally, N, S-CDs-B was successfully applied in cell imaging.

Synergistic Generation of Radicals by Formic Acid/H2O2/g-C3N4 Nanosheets for Ultra-efficient Oxidative Photodegradation of Rhodamine B

Water pollution is a global challenge endangering people's health. In this work, an ultra-efficient photodegradation system of Rhodamine B (RhB) has been established using a graphitic carbon nitride nanosheet (CNNS) as the semiconductor photocatalyst, from which energy is harvested on both the conduction band and valence band by formic acid and hydrogen peroxide, respectively. The optimized FA/H₂O₂/CNNS system increases the apparent photodegradation rate of RhB by 25 folds, from 0.0198 to 0.4975 min^-1. Through a comprehensive investigation with reactive oxygen species scavengers, electron paramagnetic resonance, high-performance liquid chromatography-mass spectrometry, etc., an oxidative mechanism for RhB photodegradation has been proposed, which combines enhanced charge carrier migration and synergistic generation of multiple radicals. Comparable performance improvements have also been observed for similar systems with different semiconductors, suggesting that such a catalytic system could afford a general approach to enhance semiconductor-catalyzed photodegradation.

Current advances on g-C3N4-based fluorescence detection for environmental contaminants

The development of highly-sensitive fluorescence detection systems for environmental contaminants has become high priority research in the past years. Special attention has been paid to graphitic carbon nitride (g-C₃N₄)-based nanomaterials, whose unique and superior optical property makes them promising and attractive candidates for this purpose. It is necessary to enhance the current understanding of the various classes of g-C₃N₄-based fluorescence detection systems and their mechanisms, as well as find suitable approaches to improve detection performance for environmental monitoring, protection, and management. In this review, the recent progresses on g-C₃N₄-based fluorescence detections for environmental contaminants, mainly including their basic principles, mechanisms, applications, modification strategies, and conclusions, are summarized. A particular emphasis is placed on the design and development of modification strategies for g-C₃N₄ with the objective of improving detection performance. High photoluminescence quantum yield, tunable fluorescence emission characteristics, and strong adsorption capacity of g-C₃N₄ could ensure the ultrasensitivity and selectivity of fluorescence detection of environmental contaminants. Concluding perspectives on the challenges and opportunities to design highly efficient g-C₃N₄-based fluorescence detection system are intensively put forward as well.

Test study and molecular dynamics simulation of Fe3+ modified TiO2 absorbing automobile exhaust

With the growth of the economy, the number of automobiles on the road is fast growing, resulting in substantial environmental pollution from exhaust gas emissions. In the automobile factory, some improvements have been achieved by constructing devices to degrade automobile exhaust. However, although most of the vehicle exhaust emissions have met the national standards, the exhaust gas is superimposed at the same time period due to the increasing traffic volume, making the exhaust emissions seriously reduce the air quality. Therefore, the scholars in the road field began to study new road materials to degrade vehicle exhaust, which has gradually become one of the effective ways to reduce automobile exhaust. Photocatalyst materials have been widely concerned because of their ability to oxidize harmful gases by solar photocatalysis. Yet, the effect has been not satisfactory because of the small light response range of photocatalyst material, which restricts the catalytic effect. In this study, this paper attempts to use Fe3+ to modify the TiO2, which is one of the main photocatalytic materials, to expand the range of light reaction band and to improve the degradation effect of automobile exhaust. The degradation effects of ordinary TiO2 and modified TiO2 on automobile exhaust were compared by test system in the laboratory. The results show that the modified TiO2 can effectively improve the performance of vehicle exhaust degradation. Moreover, the molecular dynamics method was used to establish the channel model of TiO2, and the dynamic process of automobile exhaust diffusion and absorption was simulated. The diffusion law and adsorption process of different types of automobile exhaust gas such as NO, CO, and CO2 in the TiO2 channel were analyzed from the molecular scale through the radial concentration distribution and adsorption energy.