A novel MIL-125(Ti)-based nanocomposite for enhanced adsorption and catalytic degradation of tetracycline hydrochloride: Synergetic mechanism of calcination and the nitrogen-containing reticulated surface layer

A multi-nitrogen conjugated organic molecule (TPE-2Py) was selected to surface modify the calcined MIL-125(Ti) to prepare a nanocomposite (TPE-2Py@DSMIL-125(Ti)) for adsorption and photodegradation of organic pollutant (tetracycline hydrochloride) under visible light. A novel reticulated surface layer was formed on the nanocomposite, and the adsorption capacity of TPE-2Py@DSMIL-125(Ti) for tetracycline hydrochloride can reach 157.7 mg/g under neutral conditions, which is higher than that of most other reported materials. Kinetic and thermodynamic studies show that the adsorption is a spontaneous heat absorption process, dominated by chemisorption, in which electrostatic interaction, π-π conjugation and Ti-N covalent bonds played dominant roles. The photocatalytic study shows that the visible photo-degradation efficiency of TPE-2Py@DSMIL-125(Ti) for tetracycline hydrochloride can further reach 89.1% after adsorption. Mechanism studies reveal that •O₂^- and h⁺ play a major role in the degradation process, and the separation and transfer rate of photo-generated carriers increase, improving its visible photocatalytic performance. This study revealed the relationship between the adsorption/photocatalytic properties of the nanocomposite and the structure of the molecular as well as the calcination, providing a convenient strategy to regulate the removal efficiency of MOFs materials towards organic pollutants. Furthermore, TPE-2Py@DSMIL-125(Ti) exhibits good reusability and even better removal efficiency for tetracycline hydrochloride in real water samples, indicating its sustainable treatment of pollutants in contaminated water.

Multi-channel charge transfer of hierarchical TiO2 nanosheets encapsulated MIL-125(Ti) hollow nanodisks sensitized by ZnSe for efficient CO2 photoreduction

Metal-organic frameworks-based hybrids with desirable components, structures, and properties have been proven to be promising functional materials for photocatalysis and energy conversion applications. Herein, we proposed and prepared ZnSe sensitized hierarchical TiO₂ nanosheets encapsulated MIL-125(Ti) hollow nanodisks with sandwich-like structure (MIL-125(Ti)@TiO₂\ZnSe HNDs) through a successive solvothermal and selenylation reaction route using the as-prepared MIL-125(Ti) nanodisks as precursor. In the ternary MIL-125(Ti)@TiO₂\ZnSe HNDs hybrid, TiO₂ nanosheets were transformed from MIL-125(Ti) and in situ grown on both sides of the MIL-125(Ti) shell, forming sandwich-like hollow nanodisks, and the ratio of MIL-125(Ti)/TiO₂ can be tuned by changing the solvothermal time. The ternary hybrids possess the advantages of enhanced incident light utilization and abundant accessible active sites originating from bimodal pore-size distribution and hollow sandwich-like heterostructure, which can effectively promote CO₂ photoreduction reaction. Especially, the formed multi-channel charge transfer routes in the ternary heterojunctions contribute to the charge transfer/separation and extend the lifespan of charge-separated state, thus boosting CO₂ photoreduction performance. The CO (513.1 μmol g^-1h^-1) and CH₄ (45.1 μmol g^-1h^-1) evolution rates over the optimized ternary hybrid were greatly enhanced compared with the single-component and binary hybrid photocatalysts.

De novo synthesis of photocatalytic bifunctional MIL-125(Ti)/gC3N4/RGO through sequential self-assembly and solvothermal route

In this study we have synthesized a heterostructured metal organic framework (MOF) consisting of self-assembled porous carbon nitride (gC₃N₄) and, reduced graphene oxide (RGO) with MIL-125(Ti) (CN-GO-MIL) through a simple synthesis route. As-synthesized CN-GO-MIL was characterized to determine its morphological, surface, structural, and optical properties. The synthesis produced a porous nanomaterial with efficient visible light capture and electron transport. CN-GO-MIL proved 2.23 and 1.23 times as effective as bare MIL-125(Ti) for Rhodamine B (RhB) degradation and chromium (Cr) reduction, respectively. We propose a governing photocatalytic degradation and reduction mechanism in which superoxide plays a major role in the photocatalytic degradation, followed by O₂¹, OH·, and holes, and identify methanol as a suitable hole scavenger for reduction of Cr. Moreover, Cr reduction can be best achieved at pH 2 in the presence of methanol. Performance of material in terms of apparent quantum yield (AQY), figure of merit (FOM), and catalyst surface efficiency (S.E), suggests 5% CN-GO-MIL is an efficient photocatalyst for degradation of RhB. Comparison of the AQY with previously reported MOF-based composites shows that the as synthesized 5% CN-GO-MIL can be regarded as one of best performing photocatalyst under visible light irradiation for abatement of organic and inorganic pollution.

Metal-organic frameworks derived C/TiO2 for visible light photocatalysis: Simple synthesis and contribution of carbon species

A series of in-situ carbon-doped TiO₂ (C_x/TiO₂) composites with a porous and crystalline structure were successfully synthesized via one-step and low-temperature calcination of titanium metal-organic framework (MOF), MIL-125(Ti). The resultant materials were comprehensively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption measurements, UV-vis diffuse reflectance spectrum (DRS), photoluminescence (PL) spectra and photoelectrochemical measurements, and their photocatalytic activities for bisphenol A (BPA) degradation were assessed. Compared with the benchmark TiO₂ photocatalyst (P25), the C_x/TiO₂ composite material with high specific surface, lower band gap, and reduced photogenerated electron hole ratio exhibited outstanding photodegradation activity and durability for BPA, which could be attributed to the combined effect of co-doping of multiple carbon species (substituent carbon and carbonate) and porous structure. During BPA degradation, the holes and superoxide radicals were the primary role oxidative species in the reaction process. Therefore, this new efficient photocatalyst is promising candidate for photodegradation of organic pollutants.

Heterostructured g-CN/TiO2 Photocatalysts Prepared by Thermolysis of g-CN/MIL-125(Ti) Composites for Efficient Pollutant Degradation and Hydrogen Production

Photocatalysts composed of graphitic carbon nitride (g-CN) and TiO₂ were efficiently prepared by thermolysis of the MIL-125(Ti) metal organic framework deposited on g-CN. The heterojunction between the 12 nm-sized TiO₂ nanoparticles and g-CN was well established and the highest photocatalytic activity was observed for the g-CN/TiO₂ (3:1) material. The g-CN/TiO₂ (3:1) composite exhibits high visible light performances both for the degradation of pollutants like the Orange II dye or tetracycline but also for the production of hydrogen (hydrogen evolution rate (HER) up to 1330 μmolh⁻¹g⁻¹ and apparent quantum yield of 0.22% using NiS as a cocatalyst). The improved visible light performances originate from the high specific surface area of the photocatalyst (86 m²g⁻¹) and from the efficient charge carriers separation as demonstrated by photoluminescence, photocurrent measurements, and electrochemical impedance spectroscopy. The synthetic process developed in this work is based on the thermal decomposition of metal organic framework deposited on a graphitic material and holds huge promise for the preparation of porous heterostructured photocatalysts.