Magnetic Nitrogen-Rich UiO-66 Metal-Organic Framework: An Efficient Adsorbent for Water Treatment

The postsynthetic modification of metal-organic frameworks (MOFs) has opened up a promising area to widen their water treatment application. However, their polycrystalline powdery state still restricts their widespread industrial-scale applications. Herein, the magnetization of UiO-66-NH₂ is reported as a promising approach to facilitate the separation of the used MOFs after water treatment. A two-step postmodification procedure employing 2,4,6-trichloro-1,3,5-triazine (TCT) and 5-phenyl-1H-tetrazole (PTZ) agents was introduced to level up the adsorption performance of the magnetic nanocomposite. Despite a decrement in porosity and specific surface area of the designed MOFs (m-UiO-66-TCT) compared to neat UiO-66-NH₂, it outweighs in adsorption capacity. It was observed that m-UiO-66-TCT has an adsorption capacity of ≈298 mg/g for methyl orange (MO) with facile MOF separation using an external magnet. Pseudo-second-order kinetic model and Freundlich isotherm models suitably interpret the experimental data. Thermodynamic studies showed that MO removal using m-UiO-66-TCT is spontaneous and thermodynamically favorable at higher temperatures. The m-UiO-66-TCT composite exhibited easy separation, high adsorption capacity, and good recyclability, rendering it an attractive candidate for the adsorptive removal of MO dye from aqueous environments.

Amino-Functionalized MXene Nanosheets Doped with Ce(III) as Potent Nanocontainers toward Self-Healing Epoxy Nanocomposite Coating for Corrosion Protection of Mild Steel

MXene sheets, as new 2D nanomaterials, have been used in many advanced applications due to their superior thin-layered architecture, as well as their capability to be employed as novel nanocontainers for advanced applications. In this research, intercalated Ti₃C₂ MXene sheets were synthesized through an etching method, and then they were modified with 3-aminopropyltriethoxysilane (APTES). Cerium cations (Ce³⁺) as an eco-friendly corrosion inhibitor were encapsulated within Ti₃C₂ MXene sheets to fabricate novel self-healing epoxy nanocomposite coatings. The corrosion protection performance (CPP) of Ce³⁺-doped Ti₃C₂ MXene nanosheets (Ti₃C₂ MXene-Ce³⁺) in a 3.5 wt % sodium chloride (NaCl) solution was studied on bare mild steel substrates using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements. The self-healing CPP of epoxy coatings loaded with 1 wt % undoped and doped Ti₃C₂ MXene was evaluated using EIS, salt spray, and field emission scanning electron microscopy (FE-SEM) techniques. The introduction of Ti₃C₂ MXene-Ce³⁺ into the corrosive solution and artificially scribed epoxy coating enhanced the total impedance from 717 to 6596 Ω cm² and 8876 to 32092 Ω cm², respectively, after 24 h of immersion compared to the control samples.

Recent developments in MnO2-based photocatalysts for organic dye removal: a review

The textile industry consumes a large volume of organic dyes and water. These organic dyes, which remained in the effluents, are usually persistent and difficult to degrade by conventional wastewater treatment techniques. If the wastewater is not treated properly and is discharged into water system, it will cause environmental pollution and risk to living organisms. To mitigate these impacts, the photo-driven catalysis process using semiconductor materials emerges as a promising approach. The semiconductor photocatalysts are able to remove the organic effluent through their mineralization and decolorization abilities. Besides the commonly used titanium dioxide (TiO₂), manganese dioxide (MnO₂) is a potential photocatalyst for wastewater treatment. MnO₂ has a narrow bandgap energy of 1~2 eV. Thus, it possesses high possibility to be driven by visible light and infrared light for dye degradation. This paper reviews the MnO₂-based photocatalysts in various aspects, including its fundamental and photocatalytic mechanisms, recent progress in the synthesis of MnO₂ nanostructures in particle forms and on supporting systems, and regeneration of photocatalysts for repeated use. In addition, the effect of various factors that could affect the photocatalytic performance of MnO₂ nanostructures are discussed, followed by the future prospects of the development of this semiconductor photocatalysts towards commercialization.

Physicochemical evaluation and in vitro hemocompatibility study on nanoporous hydroxyapatite

Hydroxyapatite is an ideal biomaterial for bone tissue engineering due to its biocompatibility and hemocompatibility which have been widely studied by many researchers. The incorporation of nanoporosity into hydroxyapatite could transform the biomaterial into an effective adsorbent for uremic toxins removal especially in artificial kidney system. However, the effect of nanoporosity incorporation on the hemocompatibility of hydroxyapatite has yet to be answered. In this study, nanoporous hydroxyapatite was synthesized using hydrothermal technique and its hemocompatibility was determined. Non-ionic surfactants were used as soft templates to create porosity in the hydroxyapatite. The presence of pure hydroxyapatite phase in the synthesized samples is validated by X-ray diffraction analysis and Fourier transform infrared spectroscopy. The TEM images show that the hydroxyapatite formed rod-like particles with the length of 21-90 nm and diameter of 11-70 nm. The hydroxyapatite samples exhibit BET surface area of 33-45 m² g^-1 and pore volume of 0.35-0.44 cm³ g^-1. The hemocompatibility of the hydroxyapatite was determined via hemolysis test, platelet adhesion, platelet activation and blood clotting time measurement. The nanoporous hydroxyapatite shows less than 5% hemolysis, suggesting that the sample is highly hemocompatible. There is no activation and morphological change observed on the platelets adhered onto the hydroxyapatite. The blood clotting time demonstrates that the blood incubated with the hydroxyapatite did not coagulate. This study summarizes that the synthesized nanoporous hydroxyapatite is a highly hemocompatible biomaterial and could potentially be utilized in biomedical applications.

Conversion and characterization of activated carbon fiber derived from palm empty fruit bunch waste and its kinetic study on urea adsorption

Urea removal is an important process in household wastewater purification and hemodialysis treatment. The efficiency of the urea removal can be improved by utilizing activated carbon fiber (ACF) for effective urea adsorption. In this study, ACF was prepared from oil palm empty fruit bunch (EFB) fiber via physicochemical activation using sulfuric acid as an activating reagent. Based on the FESEM result, ACF obtained after the carbonization and activation processes demonstrated uniform macropores with thick channel wall. ACF was found better prepared in 1.5:1 acid-to-EFB fiber ratio; where the pore size of ACF was analyzed as 1.2 nm in diameter with a predominant micropore volume of 0.39 cm³ g^-1 and a BET surface area of 869 m² g^-1. The reaction kinetics of urea adsorption by the ACF was found to follow a pseudo-second order kinetic model. The equilibrium amount of urea adsorbed on ACF decreased from 877.907 to 134.098 mg g^-1 as the acid-to-fiber ratio increased from 0.75 to 4. During the adsorption process, the hydroxyl (OH) groups on ACF surface were ionized and became electronegatively charged due to the weak alkalinity of urea solution, causing ionic repulsion towards partially anionic urea. The ionic repulsion force between the electronegatively charged ACF surface and urea molecules became stronger when more OH functional groups appeared on ACF prepared at higher acid impregnation ratio. The results implied that EFB fiber based ACF can be used as an efficient adsorbent for the urea removal process.

Sol–gel hydrothermal synthesis of microstructured CaO-based adsorbents for CO2capture

A novel 3D hierarchical CaCO₃hollow microspherical adsorbent composed of 1D spike-shaped nanorods was synthesized by a sol–gel hydrothermal method for CO₂capture.

In situ doping of ZnO nanowires using aerosol-assisted chemical vapour deposition

An in situ doping approach of producing Al-doped ZnO NWs was demonstrated using an aerosol-assisted chemical vapour deposition (AA-CVD) technique. In this technique, Zn precursor was kept in the middle of a horizontal tube furnace whereas the dopant solution was kept in an aerosol generator, which was located outside the furnace. The Al aerosol was flowed into the reactor during the growth of NWs in order to achieve in situ doping. Al-doped ZnO NWs were synthesized as verified by the combination of XRD, TEM/EDS and TOF-SIMS analysis. Highly (00.2) oriented ZnO seed layers were used to promote vertically aligned growth of Al-doped ZnO NWs. Lastly, a growth mechanism of vertically aligned Al-doped ZnO NWs was discussed.

Preferential growth of ZnO thin films by the atomic layer deposition technique

Preferred orientation of ZnO thin films deposited by the atomic layer deposition (ALD) technique could be manipulated by deposition temperature. In this work, diethyl zinc (DEZn) and deionized water (H(2)O) were used as a zinc source and oxygen source, respectively. The results demonstrated that (10.0) dominant ZnO thin films were grown in the temperature range of 155-220 °C. The c-axis crystal growth of these films was greatly suppressed. Adhesion of anions (such as fragments of an ethyl group) on the (00.2) polar surface of the ZnO thin film was believed to be responsible for this suppression. In contrast, (00.2) dominant ZnO thin films were obtained between 220 and 300 °C. The preferred orientations of (10.0) and (00.2) of the ZnO thin films were examined by XRD texture analysis. The texture analysis results agreed well with the alignments of ZnO nanowires (NWs) which were grown from these ZnO thin films. In this case, the nanosized crystals of ZnO thin films acted as seeds for the growth of ZnO nanowires (NWs) by chemical vapor deposition (CVD) process. The highly (00.2) textured ZnO thin films deposited at high temperatures, such as 280 °C, contained polycrystals with the c axis perpendicular to the substrate surface and provided a good template for the growth of vertically aligned ZnO NWs.