Titanium-based Metal-organic Framework Research Articles

A new sensitive layer based on clcinated Zn/Ti-MOF/magnetic molecularly imprinted polypyrrole: Application to preconcentration and electrochemical determination of perfluorooctane sulfonic acid by magnetic carbon paste electrode

In this research, a new approach based on magnetic electrodes has been developed for the determination of per-fluorooctane sulfonic acid (PSOF). Zinc and Titanium-based Metal-organic framework (MOF) was synthesized and used with polypyrrole as a conductive polymer for preparation of the absorbent to achieve the best performance for electrochemical application. The response of the electrode for determination of the PFOS was affected and optimized by different factors such as buffer solution, pH of the solution, amount of absorbent, extraction time of absorbent, accumulation time, as well as the Square Wave Voltammetry (SWV) instrumental parameters including voltage step, pulse amplitude, frequency and resting time. In the optimum condition, the response of the Zn/Ti/C-MOF-magnetic molecular imprinting polymer/carbon paste electrode (MOFMMIP/CPE) has increased logarithmically by increasing the concentration in the range of 0.002–165 μM by the limit of detection (LOD) of 0.7 nM. The obtained percentage of Recovery (96.00–104.14 %), Bias (–4.00 - 4.14 %) and Relative Standard Deviation (RSD) (1.89–3.74 %) for determination of the PFOS in real and spiked tap water, river water and well water samples demonstrates that the proposed method has an acceptable precision. The comparison between the gained data by the presented method and High-performance liquid chromatography (HPLC) showed that the presented method has high accuracy.

Catalytic open metal sites in Ti-MOFs obtained through plasma treatment for oxidative desulfurization

Titanium-based metal–organic frameworks (Ti-MOFs) are known for their redox catalytic potential, inherently limited by coordination saturation. Defect engineering introduces the unsaturated metal sites, but introducing defects for improved performance is challenging due to titanium's hydrolysis tendency and the absence of stable Ti-clusters. This study employs an Ar plasma post-synthesis treatment, adjusting defect quantities by varying duration and intensity. The resulting plasma-induced defective MUV-10, with nearly 50 % missing linkers per cluster, displays heightened catalytic activity in oxidative desulfurization. This activity directly correlates with missing linker numbers, emphasizing the superior activity of defective open sites. Defect formation enhances intrinsic activity around unsaturated metal catalytic sites, rather than increasing active site density. This defect-generation method is adaptable to other Ti-MOFs and potentially to diverse MOFs.

MIL-125-NH2 functionalized chitin scaffold as dual sorbent and photocatalyst filter for degradation of trimethoprim

A porous, photocatalytically active, and water-stable composite filter has been developed based on MIL-125-NH2, a Titanium-based Metal-Organic Framework (MOF) and chitin polymeric scaffold. In order to tune the structure and functional properties of the CH/MOF composites, the loading degree of the MOF within the polymer was systematically varied. The composite material optimal performance was achieved with a 10% wt/wt loading of MIL-125-NH2 into the chitin scaffold. This composite material was able to capture and photodegrade Trimethoprim (TMP) under acid and alkaline conditions with outstanding efficiency (82% within 180min), as well as in waters collected from different geographical locations nearby Buenos Aires that were spiked with TMP. Furthermore, the chemical stability of MIL-125-NH2 is significantly improved when incorporated into the chitin scaffold, maintaining its structural integrity even after four cycles of reactivation and reusability. The study outlines the experimental procedures for synthesizing MIL-125-NH2, preparing chitin hydrogel and nanostructured composites, and details on the adsorption and photocatalysis experiments. The practical application of our approach can be further expanded to prevent degradation during gas or liquid adsorption processes of hydrolytically unstable MOFs.

CdS quantum dots sensitized Ti-MOFs as high-performance photocathodic materials for immunoassay of alpha-fetoprotein based on Ag+ exchange strategy

Cathodic photoelectrochemical (PEC) analysis has drawn much attention because of its excellent anti-interference capability toward reductive substances in samples, but the development high-performance photocathodic materials is challenging. We report here CdS quantum dots (QDs) sensitized titanium-based metal–organic frameworks (Ti-MOFs) as high-performance photocathodic materials for ultrasensitive immunoassay of alpha-fetoprotein (AFP) based on Ag+ exchange strategy. Due to the excellent sensitization effect of CdS QDs, the photocathodic current of CdS QDs decorated MIL-125-NH2(Ti) is 25-fold that of MIL-125-NH2(Ti) alone. The photocathodic current of CdS/MIL-125-NH2(Ti) can be quenched after Ag+ exchange, because CdS is partially converted to Ag2S that serves as a charge-recombination center. Based on the PEC response of CdS/MIL-125-NH2(Ti) to Ag+, a cathodic PEC immunoassay platform is constructed for AFP detection by using CdS/MIL-125-NH2(Ti) as the photoactive material and Ag nanoparticles modified SiO2 nanospheres as labels. The linear range for AFP detection is from 1.0 × 10−4 to 1.0 × 102 ng mL−1, and the detection limit is 20 fg mL−1. The constructed PEC immunosensor is successfully used for detecting AFP in human serum samples. In this work, a novel and high-performance photoactive material is developed for cathodic PEC analysis, and a simple and effective PEC immunoassay platform for AFP detection is constructed based on Ag+ exchange strategy.

Titanium-based metal-organic frameworks as pH-responsive drug delivery carriers of 5-Fluorouracil

In this study, we synthesized two titanium-based metal-organic frameworks (Ti-MOFs), namely MIL-125 and MIL-125-NH2, known for their excellent biocompatibility, as potential carriers for the anti-cancer drug 5-Fluorouracil (5-FU). We conducted comprehensive examinations of their morphologies, particle size distributions using SEM, stability, permanent porosity, and in vitro drug loading and release behaviors. Both materials demonstrated significant advantages due to their excellent stability, large surface area, and nanoscale sizes, which resulted in a high capacity for loading 5-FU. Significantly, both MIL-125 and MIL-125-NH2 consistently displayed pH-responsive release of 5-FU. This result may not only help to enhance the therapeutic efficacy of 5-FU but is also expected to improve its targeting potential. Our current research suggests that Ti-MOFs hold great promise as carriers for 5-FU in cancer treatment, offering guidance for the design and development of new customized and responsive drug delivery system.

Hydrophobic Porphyrin Titanium-Based MOFs for Visible-Light-Driven CO2 Reduction to Formate.

Three hydrophobic porphyrin titanium-based metal-organic frameworks (MOFs) (HPA/DGIST-1, DPA/DGIST-1, and OPA/DGIST-1) were synthesized through a postsynthetic coordination reaction by using alkylphosphonic acid of different lengths (HPA, hexylphosphonic acid; DPA, dodecylphosphonic acid; OPA, octadecylphosphonic acid). Compared with the hydrophilic DGIST-1, modified DGIST-1 exhibits excellent hydrophobicity and presents good stability in humid atmospheres. Due to the introduction of porphyrin ligands, HPA/DGIST-1, DPA/DGIST-1, and OPA/DGIST-1 showed good visible-light absorption (380-700 nm) and sensitive photogenerated charge responses. When acted as catalysts, these hydrophobic Ti-MOFs can selectively reduce CO2 to HCOO- under visible-light irradiation with average reaction rates of 150.9, 178.5, and 228.3 μmol·h-1·g-1, where these values are 1.3-2.0 times higher than the system mediated by the initial porphyrin Ti-MOF catalyst. 13C NMR spectroscopy demonstrates that the catalytic product HCOO- anion originates from the reactant CO2. The photocatalytic experiments, electron paramagnetic resonance, and photoluminescence spectra tests showed that porphyrin ligands and Ti-O units can act as catalytic activity centers to realize the conversion of CO2 to HCOO-. This work demonstrated that the combination of porphyrin titanium-based MOF and alkyl hydrophobic groups is an effective way to enhance the stability of titanium-based MOFs and maintain their high photocatalytic performance.

High adsorption of ammonia in a titanium-based metal-organic framework.

We report the high adsorption of NH3 in a titanium-based metal-organic framework, MFM-300(Ti), comprising extended [TiO6]∞ chains linked by biphenyl-3,3',5,5'-tetracarboxylate ligands. At 273 K and 1 bar, MFM-300(Ti) shows an exceptional NH3 uptake of 23.4 mmol g-1 with a record-high packing density of 0.84 g cm-3. Dynamic breakthrough experiments confirm the excellent uptake and separation of NH3 at low concentration (1000 ppm). The combination of in situ neutron powder diffraction and spectroscopic studies reveal strong, yet reversible binding interactions of NH3 to the framework oxygen sites.

Synthesis and Analysis of Titanium Based Metal Organic Frameworks for Photocatalysis

Metal-Organic Frameworks (MOFs) are porous inorganic networks that have recently shown potential in energy applications as photocatalysts. The porosity of MOFs make them excellent for guest-host interactions, however, most MOFs are slightly insulating due to metal oxide nodes, resulting in larger band gaps and poor conductivity. In order to combat these issues, post-synthetic modifications (PSM) can be used to slightly alter MOF properties. In this study, PSM’s were introduced to Titanium-based MOFs with MIL topology, such as MIL-125 and MIL-125-NH2, to improve their ability to photocatalytically degrade organic dyes through the addition of polyaniline nanofibers and additional metal interactions. The performance of these modified MOFs were tested and compared to the unmodified MOFs. In addition, titanium-based MOFs, were investigated because their nodes that are more semiconducting than other MOF types. Each MOF was characterized using BET surface area analysis, infrared spectroscopy, and powder X-ray diffraction. The conductivity of different MOFs were compared using cyclic voltammetry. The relative photocatalytic properties of each MOF was determined by monitoring their efficiency for photocatalytic degradation of rhodamine B and phenol red dyes in solution under controlled environments.

Silver Nanoparticle-Loaded Titanium-Based Metal-Organic Framework for Promoting Antibacterial Performance by Synergistic Chemical-Photodynamic Therapy.

The abuse of antibiotics leads to an increasing emergence of drug-resistant bacteria, which not only causes a waste of medical resources but also seriously endangers people's health and life safety. Therefore, it is highly desirable to develop an efficient antibacterial strategy to reduce the reliance on traditional antibiotics. Antibacterial photodynamic therapy (aPDT) is regarded as an intriguing antimicrobial method that is less likely to generate drug resistance, but its efficiency still needs to be further improved. Herein, a robust titanium-based metal-organic framework ACM-1 was adopted to support Ag nanoparticles (NPs) to obtain Ag NPs@ACM-1 for boosting antibacterial efficiency via synergistic chemical-photodynamic therapy. Apart from the intrinsic antibacterial nature, Ag NPs largely boost ROS production and thus improve aPDT efficacy. As a consequence, Ag NPs@ACM-1 shows excellent antibacterial activity under visible light illumination, and its minimum bactericidal concentrations (MBCs) against E. coli, S. aureus, and MRSA are as low as 39.1, 39.1, and 62.5 μg mL-1, respectively. Moreover, to expand the practicability of Ag NPs@ACM-1, two (a dense and a loose) Ag NPs@ACM-1 films were readily fabricated by simply dispersing Ag NPs@ACM-1 into heated aqueous solutions of edible agar and sequentially cooling through heating or freeze-drying, respectively. Notably, these two films are mechanically flexible and exhibit excellent antibacterial activities, and their antimicrobial performances can be well retained in their recyclable and remade films. As agar is nontoxic, degradable, inexpensive, and ecosustainable, the dense and loose Ag NPs@ACM-1 films are potent to serve as recyclable and degradable antibacterial plastics and antibacterial dressings, respectively.

Pushing the heterometal doping limit while preserving long-lived charge separation in a Ti-based MOF photocatalyst

This study explores the nature, dynamics, and reactivity of the photo-induced charge separated excited state in a Fe3+-doped titanium-based metal organic framework (MOF), xFeMIL125-NH2, as a function of iron concentration. The MOF is synthesized with doping levels x = 0.5, 1 and 2 Fe node sites per octameric Ti-oxo cluster and characterized by powder x-ray diffraction, UV-vis diffuse reflectance, atomic absorption, and steady state Fe K-edge X-ray absorption spectroscopy. For each doping level, time-resolved X-ray transient absorption spectroscopy studies confirm the electron trap site role of the Fe sites in the excited state. Time scan data reveal multiexponential decay kinetics for the charge recombination processes which extend into the microsecond range for all three concentrations. A series of dye photodegradation studies, based on the oxidative decomposition of Rhodamine B, demonstrates the reactivity of the charge separated excited state and the photocatalytic capacity of these MOF materials compared to traditional heterometal-doped semiconductor photocatalysts.

A novel nanogold sol SERS/RRS dual-mode assay for trace imidacloprid with Ti3C2Tx@Ti-MOFs/peptide bifunctional nanoprobe

The development of rapid, simple, and highly sensitive analytical methods for detecting pesticide residues is crucial for safeguarding the environment and human health. In this study, MXeneTi3C2Tx nanosheets are used to load a titanium-based metal-organic framework (Ti-MOFs) and imidacloprid peptide (PTIMI), and a novel bifunctional nanoprobe (TN@Ti-MOFs/PT) is prepared by irradiation in a domestic microwave oven and stirring at room temperature. Powder X-ray diffraction, transmission electron microscope and Fourier transform infrared spectrometer are used to characterize the prepared nanomaterials. It is found that TN@Ti-MOFs/PT not only specifically recognizes imidacloprid (IMI), but also catalyzes the nanogold indicator reaction to generate gold nanoparticles (AuNP) in an 80 ℃ constant temperature water bath. The generated AuNP can be directly used as an optical probe for resonance Rayleigh scattering (RRS) at wavelength of 370 nm. In the presence of the Victoria blue 4 R molecule probe, it shows a robust surface enhanced Raman scattering (SERS) signal at wavelength number of 1617 cm−1. When the target molecule IMI is added, it can interact with the PTIMI specific base sequence, resulting in PT chain shedding from the TN@Ti-MOFs/PT nanoprobe surface, exposing abundant redox sites and accelerating the redox charge transfer, resulting in AuNP increase and SERS/RRS signal enhancement. As a result, a highly sensitive and specific PT-based dual-mode biosensing platform is developed for the detection of trace IMI, with a linear range of 0.01–0.25 ng/mL and a detection limit of 0.0011 and 0.0039 ng/mL by SERS and RRS assays, respectively. To demonstrate its practical application, the platform is used to detect IMI in vegetable samples, with relative deviations of 1.36–5.86% and recoveries of 95.0–107%. Additionally, the mechanism of nanocatalysis enhancement is also investigated.

A novel sandwich-type electrochemical immunosensor for sensitive detection of zearalenone using NG/PDDA/HNTs and Ti-MOF-KB composites for signal amplification

In this work, a novel sandwich-type electrochemical immunosensor based on signal amplification was developed for the ultrasensitive detection of zearalenone (ZEA). The composite consisting of poly(diallyldimethylammonium chloride) functionalized nitrogen doped graphene, halloysite nanotubes and toluidine blue (Tb/NG/PDDA/HNTs), was synthesized for the first time. Then it was modified with gold nanoparticles (AuNPs) to bind the secondary antibody (Ab2, 10 μg mL−1) and form the tracer label. In addition, ketjen black (KB) was doped into titanium-based metal–organic framework (Ti-MOF), which provided large specific surface area and employed as the sensing platform to increase the immobilization of the primary antibody (Ab1, 10 μg mL−1). This immunosensor showed a wide linear range for ZEA from 10 fg mL−1 to 100 ng mL−1 with a limit of detection (LOD) as low as 0.57 fg mL−1, which was below the maximum tolerable levels (50∼100 µg kg−1) set by the United Nations Food and Agriculture Organization (FAO).

Synthetic of functionalized magnetic titanium-based metal–organic frameworks to efficiently remove Hg(Ⅱ) from wastewater

The rapid development of process technology has led to rapid daily industrial production, which also produced a large amount of waste liquid. At the same time, the existing treatment technology cannot keep up with the demand, resulting in the malicious destruction of the environment by wastewater, especially mercury-containing wastewater was very harmful. Effective means of removing mercury ions need to be found. With magnetic ferric oxide as the core and titanium-based metal–organic frameworks as the shell, a new type of magnetic adsorbent (BTA-MIL-125(Ti)@Fe3O4) was synthesized. Materials were tested by multiple characterization methods and multiple sets of experiments. At optimal pH 6, the removal rate in 100 ppm Hg(Ⅱ) was as high as 95.8%. The theoretical adsorption capacity was 615 mg/L. Isothermal experiments, kinetic experiments and thermodynamic experiments have respectively verified that the material was a kind of adsorption material with self-emission heat based on chemical action and synergistic adsorption with Hill model. By simulating the immunity of a variety of ions (Cu, Zn, Mg, Ni, Cd), the material itself also exhibited a very high affinity for Hg(Ⅱ). The results of five high-cycle stable adsorption proved the repeatable stability of the material itself. Various characterization methods have also shown that nitrogen and sulfur-containing groups chelated with Hg(Ⅱ). All of the above was enough to show that the BTA-MIL-125(Ti)@Fe3O4 was a magnetic adsorption material with excellent performance and great prospects.

A metal-organic framework constructed by ferrocene and titanium clusters for CO2 photoreduction under visible light

As a promising photocatalyst, titanium-based metal organic framework (Ti-MOF) has been widely used for the photoreduction of CO2. In this paper, we developed a new Ti-MOF named Fe-Tc, constructed from titanium clusters and ferrocene. Fe-Tc had a wide absorbance range and a good response to visible light. Introducing ferrocene gave it good separation performance of photogenerated electrons and holes. What’s more, Fe-Tc showed excellent photocatalytic activity of CO2 photoreduction. Its production rate of formate (HCOO−) reached 39.5 μmol g−1 h−1 under visible light, which was better than some classical Ti-MOFs.

A nonradical oxidation process initiated by Ti-peroxo complex showed high specificity toward the degradation of tetracycline antibiotics

Nonradical oxidation has received wide attention in advanced oxidation processes for environmental remediation. Understanding the relationship between material characteristics and their ability to initiate nonradical oxidation processes is the key to better material design and performance. Herein, a novel titanium-based metal-organic framework MIL-125-Ti/H2O2 system was established to show a highly selective degradation efficacy toward tetracycline antibiotics. MIL-125-Ti with the abundance of TiO6 octahedra units was found to effectively activate H2O2 under dark conditions by forming an oxidative Ti-peroxo complex. The presence of the Ti-peroxo complex, confirmed by UV-visible spectrophotometer, fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy characterizations, showed superior degradation (>95% removal rate) of oxytetracycline hydrochloride (OTC), doxycycline hydrochloride, chlortetracycline hydrochloride, and tetracycline. Density functional theory calculations were performed to assist the elucidation on the mechanism of H2O2 activation and antibiotics degradation. The MIL-125-Ti/H2O2 system was highly resistant to halogens and background organics, and could well maintain its original catalytic activity in actual water matrices. It retained the ability to degrade 75% of OTC within ten test cycles. This study provides new insight into the nonradical oxidation process initiated by the unique Ti-peroxo complex of Ti-based MOF.

Titanium-based metal-organic-framework-coated SnO2 nanowires with enhanced NO2 gas sensing capability in humid environment

Herein, the NO2 gas sensing features of SnO2 nanowires (NWs) and titanium-based metal–organic framework 901 (MOF-901)-coated SnO2 NWs were investigated. Both gas sensors showed excellent selectivity to NO2. At 200 °C, the responses of SnO2 NWs and MOF-901-coated SnO2 NWs to NO2 (10 ppm) were 9.7 and 8.2, respectively. However, in a humid atmosphere, the latter nanowires showed better performance, mainly because of their hydrophobic nature and the metal–organic framework layer. At relative humidities (RHs) of 20% and higher, the MOF-901-coated sensor showed higher performance than the pristine sensor. In particular, at 80% RH, responses of 6.6 and 4.0 were obtained for these two sensors to 10 ppm NO2, respectively. Furthermore, the MOF-901-coated SnO2 NWs showed better selectivity than the other sensor. We showed that MOF-901 behaved an important role in reducing the effects of water vapor and that it can be used as a molecular sieve for enhancing the NO2 gas response of SnO2 NWs in humid environments.

NH2-MIL-125(Ti)/Reduced Graphene Oxide Enhanced Electrochemical Detection of Fenitrothion in Agricultural Products.

The abuse of organophosphate pesticides causes serious threats to human health, which threatens approximately 3 million people and leads to more than 2000 deaths each year. Therefore, it is necessary to determine the residue of fenitrothion (FT) in environmental and food samples. Herein, we developed a non-enzymatic electrochemical sensor with differential pulse voltammetry signal output to determine FT in model solutions and spiked samples. Delicately, the sensor was designed based on the fabrication of hydrothermally synthesized titanium-based metal-organic frameworks (MOFs) material (NH2-MIL-125(Ti))/reduced graphene oxide (RGO) (NH2-MIL-125(Ti)/RGO) nanocomposites for better target enrichment and electron transfer. The peak response of differential pulse voltammetry for FT under optimized conditions was linear in the range of 0.072-18 μM with the logarithm of concentrations, and the detection limit was 0.0338 μM. The fabricated sensor also demonstrated high stability and reproducibility. Moreover, it exhibited excellent sensing performances for FT in spiked agricultural products. The convenient fabrication method of NH2-MIL-125(Ti)/RGO opens up a new approach for the rational design of non-enzymatic detection methods for pesticides.

Titanium Sulfonate-Based Metal–Organic Frameworks

Titanium-based metal–organic frameworks (Ti-MOFs) are one of the most active fields of MOFs due to their intriguing catalytic properties; however, the fast reaction between the widely used carboxylate-based ligand (hard base) and Ti4+ ion (hard acid) makes the syntheses of Ti-MOFs extremely challenging. In this work, we propose a new strategy by adopting sulfonic acid (soft base) as organic ligands to synthesize Ti-MOFs based on hard and soft acid and base (HSAB) theory. As an example of this strategy, seven titanium sulfonate metal–organic frameworks have been synthesized from 1,5-naphthalenedisulfonic acid (H2nds) and titanium isopropoxide and their structures are determined by single-crystal X-ray diffraction. These compounds exhibit permanent porosity, solvent stability, and light adsorption ability with a narrow band gap (2.67 eV). This work demonstrates a powerful method for the single-crystal syntheses of new Ti-MOFs, which will greatly promote the development of Ti-MOFs.

Titanium-based metal-organic framework capsulated with magnetic nanoparticles: Antimicrobial and photocatalytic degradation of pesticides

Pesticide residues create an ecological ecosystem that is incredibly dangerous and presents major risks to human health. To solve this issue, scientists are concentrating on creating extremely effective composites with superior photocatalytic performance. Even if several efforts have been made to remove pesticides and dangerous compounds using adsorption, the development of novel adsorbents with large adsorption capabilities is still very desirable. Here, the photocatalytic of carbamate pesticides in aqueous solution under simulated sunlight irradiation in the existence of Fe3O4, CuO/Cu2O, MIL-125-NH2, Fe3O4@MIL-125-NH2 and CuO/Cu2O@MIL-125-NH2 were investigated. The photocatalytic process may be credited with the effective electron-hole separation and wider area of light response. Moreover, the mechanism of pesticide photocatalytic process was discovered as mineralization of pesticides to carbon dioxide, water, sulphate, and ammonia. Total organic carbon (TOC) analysis was used to quantify the mineralization of pesticides while UV spectroscopy was used to measure the rates of pesticides photocatalytic activity. CuO/Cu2O@MIL-125-NH2 and Fe3O4@MIL-125-NH2 composite demonstrated the maximum pesticide photocatalytic efficiency and outstanding cycle stability. The antimicrobial potency was increased and the inhibition zone was minimised when treated by a parent MIL-125-NH2 and its composites, which is surprising data when employing CuO/Cu2O@MIL-125-NH2 and Fe3O4@MIL-125-NH2 nanocomposite as an anti-bacterial material.

Enhancing the photocatalytic removal of toluene by modified porous TiO2 with internal hydrophobic interface

The efficiency and stability of photocatalytic oxidation techniques in the treatment of volatile organic compounds (VOCs) in the air are affected by the adsorption performance at the reaction interface and the photogenerated electron–hole separation efficiency. Carbon-loaded porous TiO2 with an internal hydrophobic interface was prepared by finely controlling the calcination time and temperature of a titanium-based metal–organic framework (MIL-125). The carbon load in the porous TiO2 presents a gradient from the pore surface to the interior. The formed hydrophobic interface in the channel avoids competitive adsorption between gas-phase toluene and H2O and effectively improves photogenerated electron transfer. Experiments and comprehensive analysis by using techniques such as thermogravimetric analysis, Raman spectroscopy, and ultraviolet diffuse-reflectance spectroscopy clarified the mechanism of gradient carbon formation in the porous TiO2, in which the organic ligands in MIL-125 are carbonized during calcination because of the low oxygen content of the pores. The sample prepared by pyrolyzing MIL-125 at 400 ​°C for 1 ​h showed the best activity in the photocatalytic degradation of toluene; the activity was twice that achieved with the commercial photocatalyst P25. Surface photovoltage spectroscopy and photoelectrochemical measurements proved that the gradient carbon load enhances photogenerated electron transfer in the porous TiO2. In-situ diffuse-reflectance infrared Fourier-transform spectroscopy was used to investigate the processes of photocatalytic degradation of toluene, in which the generation of C–H-containing intermediates is a crucial step. This research provides a novel concept for the future design and modification of photocatalyst structures for the effective photocatalytic degradation of VOCs.