Zirconium-based Metal-organic Framework Research Articles

Synthesis and characterization of advanced Ad-UiO-66@NGO composite for efficient CO2 capture and CO2/N2 adsorption selectivity.

Highly effective adsorbents, with their impressive adsorption capacity and outstanding selectivity, play a pivotal role in technologies such as carbon capture and utilization in industrial flue gas applications, leading to significant reductions in greenhouse gas emissions. This study aims to synthesize advanced composites via solvothermal methods, incorporating a defective Zirconium-based MOF and amine-functionalized graphene oxide. The main objective is to enhance the CO2 adsorption capacity of the composite and improve its CO2/N2 separation selectivity. The samples were characterized using XRD, FT-IR, TGA, FE-SEM, and nitrogen adsorption and desorption analysis. The composites' gas uptake capacity toward pure CO2 and N2 adsorption were tested at various temperatures and pressure ranges of 1-9 bar. The resulting amino-defective UiO-66/NGO composite containing 15 wt.% of amine-modified GO, displayed the highest CO2 uptake capacity of 15.13 mmol/g at 298 K and 9 bar, representing a remarkable 48% increase compared to the pristine MOF. Furthermore, isotherm and kinetic modeling showed a high level of agreement between the experimental data and the Freundlich and Elovich models, as indicated by their R2 values of 0.998 and 0.973, respectively. Moreover, the thermodynamic evaluation confirmed the exothermic and the spontaneity of the reaction. Furthermore, the adsorbent's CO2/N2 selectivity was evaluated using the ideal adsorbed solution theory, revealing a remarkable selectivity value of 148. The regenerability evaluation through cyclic adsorption experiments showed that the optimized composite maintained CO2 adsorption reversibility at over 81.50% after 55 adsorption-desorption cycles.

Enhanced performance of UiO-66 for supercapacitor applications through oxidation via the Hummers' method.

Supercapacitors (SCs) are gaining attention in energy storage due to their high-power density, rapid charge/discharge ability, and long life cycle. Improving these features relies on developing advanced electrode materials with better energy storage properties. This study explores UiO-66, a zirconium-based metal-organic framework (MOF), which offers advantages like a large surface area, tunable pore sizes, and stability. However, its poor electrical conductivity limits its use in supercapacitors. Herein, we applied the Hummers' method to oxidize UiO-66, creating an oxidized form, H-UiO-66, with enhanced conductivity. This material was characterized by various techniques, including SEM-EDX, XRD, XPS, FTIR, and BET analysis, while electrochemical tests (GCD, CV, and EIS) confirmed a significant improvement in specific capacitance-82.8 F g-1 for H-UiO-66 versus 0.18 F g-1 for pristine UiO-66 at 1 mA. These improvements stem from increased conductivity and electrochemical activity due to UiO-66 graphitization, highlighting the Hummers' method's effectiveness in transforming UiO-66 into a viable supercapacitor material.

Synthesis of zirconium-based metal-organic framework/gelatin aerogel for removing phosphate and fluoride from aqueous solutions.

This study describes the preparation of novel hybrid aerogels derived from gelatin (Gel), incorporating Br-functionalized zirconium-based metal-organic framework (UiO-66-Br; MOF) as modifying agent to effectively eliminate phosphate and fluoride ions from aqueous environments. The adsorption performance of MOF decorated Gel (Gel-xMOF) hybrid aerogels was investigated under different conditions, including agitation time, adsorbent dosage, solution pH, initial phosphate and fluoride concentrations, coexisting ions, and temperature. The functional groups of the gelatin network, coupled with UiO-66-Br, enhanced the adsorption performance of phosphate and fluoride ions from aqueous solutions. The structural features and physicochemical parameters were evaluated using several characterization tools. The mesoporous Gel-1.5MOF aerogels exhibited Langmuir adsorption capacities of 20.81 and 7.42 mg/g for phosphate and fluoride, respectively. Reusability and coexisting experiment results suggest that the as-prepared Gel-1.5MOF aerogels have the potential for practical applications. Electrostatic attraction and ligand exchange primarily govern the adsorption mechanism of both ions, followed by hydrogen bonding and pore-filling mechanisms. This investigation offers new insights into the successful elimination of phosphate and fluoride ions across a broad pH range.

Zr-MOF composites with zipped and unzipped carbon nanotubes for high-performance electrochemical supercapacitors.

Metal-organic frameworks (MOFs) have gained considerable interest as crystalline porous materials with notable characteristics, such as high surface area and excellent electrochemical performance, particularly in supercapacitor applications. The combination of MOFs with various nanocarbon materials further enhances their performance. This study investigated the combination of zirconium-based MOFs (Zr-MOFs) with graphene oxide nanoribbons (GONRs), zipped carbon nanotubes, and functionalized carbon nanotubes (FCNTs) to fabricate composites with elevated electrical conductivity, adjustable surface area, chemical robustness, mechanical strength, and customizable attributes for specific applications. Zr-MOFs exhibit remarkable capacitance, making them promising electrode materials for supercapacitors. GONRs and FCNTs have recently emerged as focal materials owing to their unique properties, which make them promising materials for electrochemical energy storage devices. A thorough investigation of the supercapacitive behavior of GONRs, FCNTs, Zr-MOFs, Zr-MOFs/FCNTs, and Zr-MOFs/GONRs in 1 M H2SO4 using different evaluation systems (three- and two-electrode systems) revealed a significant enhancement in the capacitance of Zr-MOFs after the introduction of GONRs and FCNTs. Employing Zr-MOF/GONR and Zr-MOF/FCNT composites as positive electrodes and GONRs as negative electrodes in two-electrode measurements demonstrated remarkable cycling stability by retaining their specific capacitances (Cs) even after 10 000 consecutive charge/discharge cycles at a high current density of 10 A g-1. Moreover, they feature a broad potential window of 1.7 V in the three-electrode system. This extends to 2 V in the two-electrode system, achieving high Cs. This highlights the remarkable electrochemical performance of the Zr-MOF/GONR and Zr-MOF/FCNT composites, offering a compelling approach for energy storage applications.

Phosphate-adsorbed metal organic framework as a recycled material for catalytic degradation of ceftriaxone sodium via peroxymonosulfate activation.

In this study, the zirconium-based metal organic framework (Zr-MOF) was applied as the adsorbent for phosphorus (P) pollution in water. Then the phosphate-adsorbed metal organic frameworks (MOFs) were used as a recycled raw material and calcined to obtain P-doped MOFs-derived carbon material (ZrP@Zr-BTC). Next, the ZrP@Zr-BTC was used for peroxymonosulfate (PMS) activation for the ceftriaxone sodium degradation. The doping of P species in the MOFs-derived carbon material led to a 31% increase in the degradation rate compared to the material without P doping (ZrO2@Zr-BTC). The characterization results confirmed that ZrP@Zr-BTC contained zirconium phosphate, ZrP and ZrO2 in addition to inorganic carbon. P doping could affect the morphology of zirconium species and the bonding state of oxygen element in the catalyst. The degradation of ceftriaxone sodium by the ZrP@Zr-BTC/PMS system could reach 96±0.82%. The ZrP@Zr-BTC material also had strong resistance to water quality interference and reusability. The electron spin resonance spectrometer (ESR) analysis indicated singlet oxygen (1O2) played an important role and other free radicals (SO4-•, •OH, O2-•) were auxiliary. The Fukui function calculated by density functional theory explained the sites susceptible to attack by reactive species, and liquid chromatography-mass spectrometry (LC-MS) results allowed for the inference of the degradation pathway of ceftriaxone sodium. This study not only provides a simple and effective method for the disposal and recycling of waste adsorbents but also offers valuable insights into the role of MOF-derived carbon in activating PMS for pollutant degradation.

Portable foodborne pathogen detection via ratiometric fluorescence nanoprobe for adenosine triphosphate quantification based on DNA-functionalized metal-organic framework.

The increasing incidence of foodborne illnesses highlights the need for rapid, sensitive, and portable methods to detect pathogenic bacteria in food. In this work, we develop a portable method that utilizes a ratiometric fluorescence nanoprobe for adenosine triphosphate (ATP) quantification. The nanoprobe is constructed by encapsulating Ru(bpy)32+ within a zirconium-based metal-organic framework, followed by functionalization of double-stranded DNA (dsDNA). This design permits SYBR Green I (SGI) to intercalate into dsDNA, conferring the nanoprobe with dual-emission property. The presence of ATP disrupts dsDNA structure, quenching SGI fluorescence while maintaining Ru(bpy)32+ fluorescence, providing a stable reference signal. This differential response enables the nanoprobe to achieve ratiometric ATP detection with high precision and sensitivity, with a detection limit of 0.63μM. Since ATP is a reliable biomarker for viable bacterial cells, a portable hydrogel kit was further developed by integrating the ratiometric fluorescence nanoprobe into an agarose hydrogel matrix. The validation of the kit was conducted using a smartphone application for color recognition, enabling the rapid and on-site detection of pathogens in milk samples. The kit exhibits exceptional sensitivity with a detection limit of 10CFU/mL, making it a promising tool for real-time bacteria detection in food safety monitoring.

Phase-Engineered Zirconium MOF-Based Titanium Single-Atom Catalysts: Phase-Dependent Properties and Applications in Biodiesel Synthesis

The paper presents a study on the development and application of zirconium-based metal-organic frameworks (Zr-MOFs) supported titanium (Ti) single-atom catalysts (SACs). The research focuses on how the phase of Zr-MOFs...

Dispersive solid phase extraction of apixaban from human plasma samples prior to capillary electrophoresis determination using zirconium-based metal organic frameworks prepared by different modulator and solvent.

Here, a zirconium-based metal organic framework-dispersive solid phase extraction method was established as an efficient, robust, and accurate approach for quantifying apixabanin human plasma samples prior to capillary electrophoresis with diode array detection. Various types of metal organic frameworks based on UiO-66-NH2 were synthesized by altering modulators and solvents and applied as sorbents in the extraction procedure. Among the tested sorbents, UiO-66-NH2 prepared in dimethylformamide in the presence of acetic acid was found to be the best sorbent in this method for the extraction of apixaban with high extraction efficiency comparable to other types of UiO-66-NH2 metal organic frameworks. The extraction and preconcentration of apixaban were carried out by adding 5mg of synthesized sorbent to a 5mL sample solution, followed by vortexing for 3min. After discarding the supernatant, the adsorbed analyte was eluted from the sorbent surface using 60µL acetonitrile under vortexing for 2min. The effective parameters of the offered method were optimized and validated using a one-parameter-at-a- time strategy. The detection and quantification limits of the method were 9.9 and 32ng mL-1 in plasma and 1.5 and 4.9ng mL-1 in deionized water, respectively. The method was linear ranging from 4.9 to 1000ng mL-1 in deionized water and from 32 to 500ng mL-1 in plasma, respectively. The enrichment factor and extraction recovery values were 44% and 53%, respectively. The relative standard deviations were ≤6.2% for intra- and inter-day precisions. Finally, the proposed method was successfully employed to quantify apixaban in human plasma samples.

Perfluoroalkyl-Functionalization of Zirconium-Based Metal–Organic Framework Nanosheets for Photosynthesis of Hydrogen Peroxide from Dioxygen and Water

Solar-light-driven photosynthesis of hydrogen peroxide (H2O2) from dioxygen (O2) and water (H2O) is a sustainable process. Metal–organic frameworks (MOFs) are promising candidates for the photosynthesis of H2O2 because of their...

Enhancing Biocatalysis: Metal-Organic Frameworks as Multifunctional Enzyme Hosts.

ConspectusEnzymes are highly efficient and selective catalysts that operate under mild conditions, making them invaluable for various chemical transformations. However, their limitations, such as instability and high cost, call for advancements in enzyme immobilization and the development of suitable host materials. Metal-organic frameworks (MOFs), characterized by high porosity, crystallinity, and tunability, are promising candidates for enzyme encapsulation. Among these, zirconium-based MOFs (Zr-MOFs) stand out due to their exceptional structural diversity and chemical stability. The physical and chemical properties of Zr-MOFs can be tuned and characterized with atomic precision, and their interactions with enzymes can be analyzed through a range of techniques spanning from chemistry and materials science to biochemistry. This tunable platform provides opportunities to systematically investigate the impact of encapsulation on the stability and activity of enzymes in order to develop design rules for enzyme hosts.In this Account, we discuss experimentally validated concepts for designing MOF hosts based on their structural properties and enzyme encapsulation mechanisms. We present methods to enhance enzyme catalytic performance through encapsulation and strategies for creating multifunctional enzyme@MOF systems via host modifications. We start by highlighting the importance of host structural design that maximizes substrate diffusion and enzyme availability, with particular focus on MOFs containing hierarchical mesoporous structures such as those in the csq topology. We then delve into the encapsulation process and host-guest interactions examined through techniques such as microscopy, calorimetry, and computational methods, which provide guidelines to fine-tune the local pore chemical environment to enhance enzyme stability and catalytic activity. Techniques found in biochemistry, such as isothermal titration calorimetry (ITC) and confocal laser scanning microscopy (CLSM), were developed to investigate enzyme encapsulation mechanisms, revealing high-entropy-driven host-guest affinity. Additionally, we discuss cases in which enzyme@MOF systems demonstrated enhanced catalytic activities and multifunctional capabilities. Encapsulated enzymes have demonstrated improved thermal and chemical stabilities compared to their free counterparts, maintaining activity under conditions that typically lead to denaturation. Additionally, the highly tunable nature of the MOF platforms allows them to support more complex systems such as tandem reactions, enabling applications in biophotocatalysis, bioelectrocatalysis, and targeted therapeutic protein delivery.The versatility of enzyme@MOFs promises extensive applications in both research and industrial processes across fields including biotechnology, pharmaceutical development, and environmental science. We provide an outlook for promising directions for enzyme@MOF research, with the aim of continuing innovation and exploration. We hope that this Account can benefit chemists, biologists, and material scientists toward designing efficient and adaptable next-generation biocatalytic composite materials.

Zirconium-based metal–organic framework immobilized subtilisin for anti-biofilm

Biofilm formation contributes significantly to bacterial drug resistance, and employing enzymes to combat biofilms is an effective way. In this study, UiO-66-NH2 was synthesized to immobilize subtilisin, resulting in enzymatic anti-biofilm composite materials. The stability, biofilm inhibition capabilities, and biological safety of the composite materials were investigated. The results demonstrated that the immobilized proteases displayed significantly enhanced thermal and pH stability compared to free subtilisin. After 30 days of storage, the immobilized enzymes maintained around 66.8 % of their activity. Furthermore, it effectively suppressed biofilm formation by Staphylococcus aureus and Escherichia coli. Importantly, it does not induce hemolysis of red blood cells or exhibit cytotoxicity, demonstrating its favorable biocompatibility. This study provides novel light on the development of enzyme-based antibiofilm agents.

A highly efficient and recyclable zirconium-based metal organic framework for the effective removal of nanoplastics from multiple aqueous environments

A highly efficient and recyclable zirconium-based metal organic framework for the effective removal of nanoplastics from multiple aqueous environments

UiO-67 metal-organic framework loaded on hardwood biochar for sustainable management of environmental boron contaminations

Boron contamination in water poses significant potential risks to human health and the environment, necessitating the development of efficient, cost-effective, and sustainable remediation technologies. This study introduces a novel composite material combining a zirconium-based metal-organic framework (UiO-67) and a low-cost carbonaceous material (hardwood biochar, BC) with synergetic efficiency to address boron-polluted waters. The UiO-67-biochar (UBC) composite exhibits effective surface chemistry and a remarkably high specific surface area of approximately 881.9m²/g, substantially increasing from the 19.7m²/g of biochar. Our experimental results demonstrate that UBC removed up to 88.5% of boron from 20 ppm polluted water, achieving levels compliant with the WHO standards. The composite also showed excellent reusability, maintaining 95% efficiency over multiple cycles without loss of crystallinity. Life cycle assessment and cost analysis indicate that an optimal MOF to biochar ratio of approximately 60wt% minimises CO2 emissions and costs while maximising the boron removal efficiency. The UiO-67-biochar composites proposed here offers a promising scalable solution for boron contamination and potentially other environmental pollutants, combining the high functionality of UiO-67 with the practical and economic advantages of biochar.

Precise manipulation of pore sizes in Zr(IV)-Based metal-organic frameworks for enhanced bisphenol a removal from water

Metal-organic frameworks (MOFs) recently gained immense popularity for the adsorption of organic impurities. In this work, the adsorptive separation of bisphenol A (BPA) from aqueous mixtures was explored utilizing three types of zirconium-based MOFs, namely MOF-808, UiO-66, and hierarchically porous UiO-66 (HP-UiO-66). The HP-UiO-66, which was etched by sodium acetate as the terminal ligand, generated large mesopores ranging from 40 to 300 Å due to the departure of partial linkers and metallic clusters. The adsorption ability for BPA increased significantly with the introduction of numerous mesopores onto the HP-UiO-66 framework, even though the surface area of HP-UiO-66 was lower compared to that of the pristine UiO-66 and MOF-808. The study revealed that the maximum adsorption capacities (q) for BPA by HP-UiO-66 reached up to 295.04 mg g−1, which was about 88.5% and 17.4% higher in comparison to UiO-66 and MOF-808, respectively. Furthermore, the q value of HP-UiO-66 was also better than many other previously reported MOF adsorbents. The analysis of possible adsorption mechanisms indicated that physical pore-filling was anticipated as the principal mechanism, attributed to the larger window size and high mesopore surface area of HP-UiO-66. Furthermore, X-ray photoelectron and Fourier transform infrared spectroscopic measurements inferred that the synergetic effects of H-bonding and π-π interactions played crucial roles in BPA capture as well. Overall, this study revealed a structure–property relationship in the Zr-MOFs-based adsorbents and opened up a new avenue to exploit unique MOF platforms for the efficient removal of emerging contaminations in the future.

Fluoride Product Inhibition: New Insight into the Degradation of Nerve Agents by Zr-MOFs.

Zirconium-based metal-organic frameworks (Zr-MOFs) have shown remarkable efficacy in catalytically degrading neurotoxic agents in recent years. However, the catalytic activity of Zr-MOFs can be inhibited due to the binding of phosphate degradation products to the Zr nodes. Here, we reported the inhibition effect of a nonphosphate substance, fluoride, which can deactivate Zr-MOF nodes for the degradation of GD and VX and simulate DEPPT. The experimental and theoretical calculation results reveal that the fluoride product during GD degradation shows much more significant suppression than phosphate. The phosphate products can depart from the Zr nodes completely by adding H2O molecules on the Zr nodes to reduce the energy barrier. However, the fluoride can replace the bridged μ3-OH groups and terminal -OH groups on Zr-oxo clusters irreversibly, changing the electric density of Zr nodes and eliminating the terminal -OH. Without the terminal -OH, the five-coordinate phosphorus intermediate cannot be formed, resulting in the inactivation of Zr-O-Zr sites. This study provides new insights into Zr-MOF catalyst deactivation mechanisms and may help to develop a new strategy to design MOFs with high anti-inhibition efficiency for the degradation of nerve agents.

Water motifs in zirconium metal-organic frameworks induced by nanoconfinement and hydrophilic adsorption sites

The intricate hydrogen-bonded network of water gives rise to various structures with anomalous properties at different thermodynamic conditions. Nanoconfinement can further modify the water structure and properties, and induce specific water motifs, which are instrumental for technological applications such as atmospheric water harvesting. However, so far, a causal relationship between nanoconfinement and the presence of specific hydrophilic adsorption sites is lacking, hampering the further design of nanostructured materials for water templating. Therefore, this work investigates the organisation of water in zirconium-based metal-organic frameworks (MOFs) with varying topologies, pore sizes, and chemical composition, to extract design rules to shape water. The highly tuneable pores and hydrophilicity of MOFs makes them ideally suited for this purpose. We find that small nanopores favour orderly water clusters that nucleate at hydrophilic adsorption sites. Favourably positioning the secondary adsorption sites, hydrogen-bonded to the primary adsorption sites, allows larger clusters to form at moderate adsorption conditions. To disentangle the importance of nanoconfinement and hydrophilic nucleation sites in this process, we introduce an analytical model with precise control of the adsorption sites. This sheds a new light on design parameters to induce specific water clusters and hydrogen-bonded networks, thus rationalising the application space of water in nanoconfinement.

Synthesis of zirconium-based metal-organic framework under mild conditions and its application to the removal of cationic and anionic dyes from wastewater

Water resources contaminated by industrial dyes can pose a significant threat to the environment and human health. Herein, we conducted a study on the removal of cationic and anionic dyes, such as methylene blue (MB) and methyl orange (MO), using MIL-140A, a zirconium-based metal-organic framework. MIL-140A is synthesized in a Schlenk flask at 120 °C, whereas its conventional synthesis route involves a teflon-sealed autoclave at 220 °C, highlighting the cost reduction and lower equipment requirements of the low-temperature synthesis. The structure of MIL-140A is characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscope (SEM), and nitrogen adsorption techniques. The optimal pH for the adsorption of two dyes by MIL-140A is pH 5–8 for MB and pH 3 for MO. The adsorption equilibrium can be reached within 60 min at room temperature, and the adsorption of both dyes on MIL-140A follows pseudo-second-order kinetics and Langmuir isotherm, and the maximum adsorption capacity of MO and MB by MIL-140A were 163.6 and 89.2 mg/g, respectively. Thermodynamic studies indicate an entropy-driven spontaneous process. The adsorption mechanism of MO and MB on MIL-140A is investigated using FT-IR and X-ray photoelectron spectroscopy. The adsorption of MO involves coordination between Zr and sulfonate, while MB adsorption occurs via π-π interactions. Additionally, MIL-140A exhibits better removal efficiency for MO from lithium battery wastewater compared to MB, primarily due to stronger coordination interactions than π-π interactions. These findings demonstrate that MIL-140A is a promising adsorbent for effectively removing both anionic and cationic dyes from water resources.

Fine-Tuning Porous Structure of Zirconium-Based Metal-Organic Frameworks for Efficient Separation and Purification of Astaxanthin by Defect Engineering.

Efficient separation of bioactive compounds from nature source, particularly that of astaxanthin (AXT), remains challenging due to their low content in complicated matrix and readily degradable structure. Herein, a modulator-induced defect engineering is presented on the stable zirconium-based metal-organic frameworks (Zr-MOFs) to optimize pore size and pore chemistry for the efficient separation and purification of AXT for the first time. High adsorption capacity of 26.21mgg-1 is achieved on the best-performing defect Zr-MOF (d-UiO-67-4), superior over the other reported adsorbent for AXT. Meanwhile, d-UiO-67-4 exhibits the selective adsorption of AXT over other carotenoids analogues with similar structure and properties. This is attributed to the preferential non-covalent interactions between defect framework and AXT revealed by the spectroscopy analysis and density functional theory (DFT) calculations. High purity of AXT with 89.0%±2.3% extraction efficiency can be realized after the purification of AXT by d-UiO-67-4. The practical separation performance of d-UiO-67-4 for AXT extracted from Haematococcus pluvialis is demonstrated by fixed-bed column-based dynamic adsorption and desorption experiments. This work broadens the preparation methods for thermosensitive active substances and provided new research ideas for the controlled adsorption of functional food factors.

Engineering Ion Affinity of Zr-MOF Hybrid PDMS Membranes for the Selective Separation of Na+/Ca2.

Ion-selective separation, especially Na+/Ca2+ separation, is of significant importance in the realms of biomimetic research and the fabrication of biomimetic devices, underscoring the pivotal role that sodium and calcium ions play in cellular metabolism. However, the analogous ionic radii and charge densities shared by sodium and calcium ions significantly impede their effective discrimination, presenting formidable challenges for the precise engineering of ion separation materials, such as separation membranes. In this study, a polydimethylsiloxane (PDMS) separation membrane hybridized with zirconium-based metal-organic frameworks (UiO-66, UiO-66-NO2 and UiO-66-NH2) was constructed. Through the meticulous design of the MOF functional groups, the material's affinity for specific ions was modulated, thereby achieving efficient Na+/Ca2+ separation. Notably, the PDMS integrated with amino-modified Zr-MOF exhibited an efficacious selective separation of Na+ and Ca2+ ions. The interaction between the amino group of UiO-66-NH2 and Ca2+ gave rise to the observed superior selectivity toward Ca2+ cations and enhanced separation efficiencies of up to 64% compared to pristine PDMS for UiO-66-NH2-embedded membranes.

Unexpected Photodriven Linker-to-Node Hole Transfer in a Zirconium-Based Metal-Organic Framework.

Zr6(μ3-O)4(μ3-OH)4 node cores are indispensable building blocks for almost all zirconium-based metal-organic frameworks. Consistent with the insulating nature of zirconia, they are generally considered electronically inert. Contrasting this viewpoint, we present spectral measurements and calculations indicating that emission from photoexcited NU-601, a six-connected Zr-based MOF, comes from both linker-centric locally excited and linker-to-node charge-transfer (CT) states. The CT state originates from a hole transfer process enabled by favorable energy alignment of the HOMOs of the node and linker. This alignment can be manipulated by changing the pH of the medium, which alters the protonation state of multiple oxy groups on the Zr-node. Thus, the acid-base chemistry of the node has a direct effect on the photophysics of the MOF following linker-localized electronic excitation. These new findings open opportunities to understand and exploit, for energy conversion, unconventional mechanisms of exciton formation and transport in MOFs.