Recent advancements in modifications of metal-organic frameworks-based materials for enhanced water purification and contaminant detection

Metal-organic frameworks (MOFs) have emerged as a key focus in water treatment and monitoring due to their unique structural features, including extensive surface area, customizable porosity, reversible adsorption, and high catalytic efficiency. While numerous reviews have discussed MOFs in environmental remediation, this review specifically addresses recent advancements in modifying MOFs to enhance their effectiveness in water purification and monitoring. It underscores their roles as adsorbents, photocatalysts, and in luminescent and electrochemical sensing. Advancements such as pore modification, defect engineering, and functionalization, combined synergistically with advanced materials, have led to the development of recyclable MOF-based nano-adsorbents, Z-scheme photocatalytic systems, nanocomposites, and hybrid materials. These innovations have broadened the spectrum of removable contaminants and improved material recyclability. Additionally, this review delves into the creation of multifunctional MOF materials, the development of robust MOF variants, and the simplification of synthesis methods, marking significant progress in MOF sensor technology. Furthermore, the review addresses current challenges in this field and proposes potential future research directions and practical applications. The growing research interest in MOFs underscores the need for an updated synthesis of knowledge in this area, focusing on both current challenges and future opportunities in water remediation.

Construction of a uniform zeolitic imidazole framework (ZIF-8) nanocrystal through a wet chemical route towards supercapacitor application

Exploring larger surface area electrode materials is crucial for the development of an efficient supercapacitors (SCs) with superior electrochemical performance. Herein, a cost-effective strategy was adopted to synthesize a series of ZIF8 nanocrystals, and their size effect as a function of surface area was also examined. The resultant ZIF8-4 nanocrystal exhibits a uniform hexagonal structure with a large surface area (2800 m2 g-1) and nanometre size while maintaining a yield as high as 78%. The SCs performance was explored by employing different aqueous electrolytes (0.5 M H2SO4 and 1 M KOH) in a three-electrode set-up. The SC performance using a basic electrolyte (1 M KOH) was superior owing to the high ionic mobility of K+. The optimized ZIF8-4 nanocrystal electrode showed a faradaic reaction with a highest capacitance of 1420 F g-1 at 1 A g-1 of current density compared to other as-prepared electrodes in the three-electrode assembly. In addition, the resultant ZIF8-4 was embedded into a symmetric supercapacitor (SSC), and the device offered 350 F g-1 of capacitance with a maximum energy and power density of 43.7 W h kg-1 and 900 W kg-1 at 1 A g-1 of current density, respectively. To determine the practical viewpoint and real-world applications of the ZIF8-4 SSC device, 7000 GCD cycles were performed at 10 A g-1 of current density. Significantly, the device exhibited a cycling stability around 90% compared to the initial capacitance. Therefore, these findings provide a pathway for constructing large surface area ZIF8-based electrodes for high-value-added energy storage applications, particularly supercapacitors.

Fabrication of Ru loaded MgB2 with guar gum hybrid for photocatalytic degradation of crystal violet

Today, dyes/pigment-based materials are confronting a serious issue in harming marine ecology. Annihilate these serious water pollutants using photoactive 2D nanohybrid catalysts showed promising comparativeness over available photocatalysts. In the present work, a facile route to decorate Ruthenium (Ru) on 2D MgB2 flower-like nanostructures was developed via ecofriendly guar gum biopolymer substantial template (MgB2/GG@Ru NFS) and its photocatalytic performance was reported. Synthesis of MgB2@Ru, MgB2/GG@Ru NFS and commercial MgB2, was studied by FTIR, XRD, FE-SEM, EDX, AFM, TEM, UV-vis spectra, and XPS analysis. From the results, the MgB2/GG@Ru NFS exhibited a superior photocatalytic performance (99.7 %) than its precursors MgB2@Ru (79.7 %), and MgB2 (53.7 %), with the degradation efficiency of the crystal violet (CV) within 100 min under visible light irradiation. The proposed photo-catalyst MgB2/GG@Ru NFS showed negligible loss of photocatalytic activity even after five successive cycles, revealing its reusability and enhanced stability due to the network structure. The photocatalytic mechanism for MgB2/GG@Ru NFS was evaluated by trapping experiment of active species, verifying that superoxide (O2-) and electron (e-) contributed significant role in the dye degradation.

A Novel Biosensing Approach: Improving SnS2 FET Sensitivity with a Tailored Supporter Molecule and Custom Substrate

The exclusive features of two-dimensional (2D) semiconductors, such as high surface-to-volume ratios, tunable electronic properties, and biocompatibility, provide promising opportunities for developing highly sensitive biosensors. However, developing practical biosensors that can promptly detect low concentrations of target analytes remains a challenging task. Here, a field-effect-transistor comprising n-type transition metal dichalcogenide tin disulfide (SnS2 ) is developed over the hexagonal boron nitride (h-BN) for the detection of streptavidin protein (Strep.) as a target analyte. A self-designed receptor based on the pyrene-lysine conjugated with biotin (PLCB) is utilized to maintain the sensitivity of the SnS2 /h-BN FET because of the π-π stacking. The detection capabilities of SnS2 /h-BN FET are investigated using both Raman spectroscopy and electrical characterizations. The real-time electrical measurements exhibit that the SnS2 /h-BN FET is capable of detecting streptavidin at a remarkably low concentration of 0.5 pm, within 13.2 s. Additionally, the selectivity of the device is investigated by measuring its response against a Cow-like serum egg white protein (BSA), having a comparative molecular weight to that of the streptavidin. These results indicate a high sensitivity and rapid response of SnS2 /h-BN biosensor against the selective proteins, which can have significant implications in several fields including point-of-care diagnostics, drug discovery, and environmental monitoring.

Metal-organic framework-based nanomaterials for CO2 storage: A review

The increasing recognition of the impact of CO2 emissions as a global concern, directly linked to the rise in global temperature, has raised significant attention. Carbon capture and storage, particularly in association with adsorbents, has occurred as a pivotal approach to address this pressing issue. Large surface area, high porosity, and abundant adsorption sites make metal-organic frameworks (MOFs) promising contenders for CO2 uptake. This review commences by discussing recent advancements in MOFs with diverse adsorption sites, encompassing open metal sites and Lewis basic centers. Next, diverse strategies aimed at enhancing CO2 adsorption capabilities are presented, including pore size manipulation, post-synthetic modifications, and composite formation. Finally, the extant challenges and anticipated prospects pertaining to the development of MOF-based nanomaterials for CO2 storage are described.

Tunning the Zeolitic Imidazole Framework (ZIF8) through the Wet Chemical Route for the Hydrogen Evolution Reaction

Utilizing zeolitic imidazolate frameworks (ZIFs) poses a significant challenge that demands a facile synthesis method to produce uniform and nanometer-scale materials with high surface areas while achieving high yields. Herein, we demonstrate a facile and cost-effective strategy to systematically produce ZIF8 nanocrystals. Typically, ZIF8 nanocrystal synthesis involves a wet chemical route. As the reaction time decreased (150, 120, and 90 min), the size of the ZIF8 crystals decreased with uniform morphology, and productivity reached as high as 89%. The composition of the product was confirmed through XRD, FE-SEM, TEM, EDS, and Raman spectroscopy. The ZIF8 synthesized with different reaction time was finally employed for catalyzing the electrochemical hydrogen evaluation reaction (HER). The optimized ZIF8-3 obtained at 90 min of reaction time exhibited a superior catalytic action on the HER in alkaline medium, along with a remarkably long-term stability for 24 h compared with the other ZIF8 nanocrystals obtained at different reaction times. Specifically, the optimized ZIF8-3 sample revealed an HER overpotential of 172 mV and a Tafel slope of 104.15 mV·dec^-1. This finding, thus, demonstrates ZIF8 as a promising electrocatalyst for the production of high-value-added green and sustainable hydrogen energy.

Titanium dioxide incorporated in cellulose nanofibers with enhanced UV blocking performance by eliminating ROS generation

The preparation of sunblocks with dispersion stability, ultraviolet blocking, and photocompatibility remains a considerable challenge. Plant-derived natural polymers, such as cellulose nanofibers (CNF), show versatile traits, including long aspect ratio, hydrophilic nature, resource abundance, and low material cost. In the present study, a facile and cost-effective strategy is reported for the fabrication of nanostructured inorganic materials by incorporating natural polymers as interspersed, systematically nanosized titanium dioxide (TiO2) particles onto CNF. Among all experiments, the optimized TiO2@CNF3 showed higher ultraviolet blocking performance and less whitening effect. The outstanding performance is attributed to the engineering of equally dispersed nano-sized TiO2 particles on the CNF surface and stable dispersion. Significantly, TiO2@CNF3 exhibited excellent compatibility with avobenzone (80%), an oil-soluble ingredient used in sunblock products, illustrating the photoprotection enhancement under ultraviolet A (UVA) and ultraviolet B (UVB). Moreover, only 14.8% rhodamine B (Rho-B) dye degraded through photocatalytic oxidation process with the TiO2@CNF3, which is negligible photocatalytic activity compared to that of TiO2 (95% dye degraded). Furthermore, commercial inorganic and organic sunblock products with SPF lifetimes of 35+ and 50+ were modified using CNF, significantly enhancing the transmittance performance compared to that of the pure sunblock. However, it was also observed that hydrophilic CNF tended to demulsify the creams due to electrostatic disequilibrium. This CNF-based modified TiO2 system is a new window to replace effective sunblock products in high-value-added applications, such as cosmetics.

Enhanced photocatalytic crystal-violet degradation performances of sonochemically-synthesized AC-CeO2 nanocomposites

Semiconductor-based photocatalysis is one of the favorable techniques for the wastewater treatment. Herein, we synthesized the activated carbon-decorated cerium dioxide (AC-CeO₂) nanocomposites via the facile ultrasonication method by using the biomass-derived AC nanoflakes and the sonochemically-synthesized CeO₂ nanoparticles. The AC-CeO₂ nanocomposites exhibited the aggregated morphology with the AC nanoflakes-anchored CeO₂ nanoparticles. Since the hybridization of conductive AC and semiconductive CeO₂ would lead to the increased photocarrier transport and the reduced photocarrier recombination, during the photocatalytic reaction, the AC-CeO₂ nanocomposites showed the enhanced crystal violet dye-degradation efficiency up to 97.9 % within 135 min. The results suggest that the AC-CeO₂ nanocomposites hold promise as a prominent photocatalyst for future green environmental technology.

Change in adsorption behavior of aquatic humic substances on microplastic through biotic and abiotic aging processes

Interactions between microplastics (MPs) and humic substances (HS) are inevitable in MP-contaminated aquatic environment because of the ubiquitous presence of HS. In this study, we explored the effects of abiotic and biotic aging processes on the adsorption behavior of aquatic HS on MPs. Aging experiments were conducted using polyethylene (PE) as a representative MP, in which UV irradiation and microbial incubation were applied for 15 to 18 days to mimic the natural abiotic and biotic aging processes. Surface modifications after the aging treatments were evidenced by the appearance of CO, CO, O-C=O, and -OH groups; the formation of grooves on UV-aged PE; and the formation of biofilms on the surface of bio-aged PE. The specific surface areas of both treated PE MPs increased with aging. Higher HS adsorption on PE surface was observed after the aging treatments, with a highest kinetic rate for UV-aged PE than that for bio-aged PE. The adsorption isotherm models revealed that the aging processes enhanced the HS adsorption tendency, as evidenced by the highest adsorption capacity for UV-aged PE (~187 μg C/m²), followed by bio-aged PE (~157 μg C/m²) and pristine PE (~87.5 μg C/m²) for a comparable extended aging period (15-18 days). The difference was more pronounced at a lower pH. The enhanced HS adsorption was mainly attributed to the formation of hydrogen bonds, whereas HS adsorption on pristine PE was dominated by hydrophobic interactions and weak van der Waals interactions. Among the two identified fluorescent components (terrestrial humic-like C1 and protein-like C2), C1 exhibited a higher affinity for adsorption onto PE irrespective of aging. Our findings provide insights into the substantial changes that occur in the interactions between MPs and aquatic organic matter with aging processes, which may alter the fate and environmental impacts of MPs in many aquatic systems.

Correction: Fabrication of Fe3O4-incorporated MnO2 nanoflowers as electrodes for enhanced asymmetric supercapacitor performance

Correction for 'Fabrication of Fe₃O₄-incorporated MnO₂ nanoflowers as electrodes for enhanced asymmetric supercapacitor performance' by Iqra Rabani et al., Dalton Trans., 2022, https://doi.org/10.1039/D2DT01942F.

Graphitic carbon-encapsulated V2O5 nanocomposites as a superb photocatalyst for crystal violet degradation

To materialize the excellent photocatalyst for crystal violet dye-degradation, the graphitic carbon-encapsulated vanadium pentoxide (GC-V₂O₅) nanocomposites were synthesized through the simple sonication method by using the green tea waste-derived GC nanoflakes and the sonochemically synthesized V₂O₅ nanorods. The nanocomposites were confirmed to comprise an aggregated morphology, in which the orthorhombic V₂O₅ nanorods were well anchored with the intertwingled GC nanoflakes. Owing to the encapsulation of defective V₂O₅ by conductive GC, the GC-V₂O₅ nanocomposites exhibited the enhanced photocatalytic dye-degradation efficiency up to 98.4% within 105 min. Namely, the encapsulated GC nanosheets might compensate the native defects (i.e., charge traps) on the V₂O₅ surface; hence, the charge transport could be enhanced during the dye-degradation process while the photocarrier recombination could be suppressed. The results suggest the conducting layer-encapsulated semiconducting oxide nanocomposites (e.g., GC-V₂O₅) to be of good use for future green environmental technology, particularly, as a superb photocatalyst for dye degradation.

Visible light-driven photocatalytic rapid degradation of organic contaminants engaging manganese dioxide-incorporated iron oxide three dimensional nanoflowers

Water pollution via hazardous organic pollutants poses a high threat to the environment and globally imperils aquatic life and human health. Therefore, the elimination of toxic organic waste from water sources is vital to ensure a healthy green environment. In the current work, we synthesized α-MnO₂-Fe₃O₄ 3D-flower like structure using a two-step hydrothermal method and explored the combination in a visible-light-assisted photocatalytic degrdation of dyes. The attained high specific surface area of 82 m²/g with mesoporous nature of α-MnO₂ and Fe₃O₄ together can generate more active sites after exposure to visible light, leading to remarkable photodegradation performance. Significantly, twofold higher dye (methylene blue, MB (94.8%/120 min; crystal violet, CV (93.7%/120 min)) and drug (LVO 91%/90 min) photodegradations were observed with α-MnO₂-Fe₃O₄ as catalyst than pure α-MnO₂ and Fe₃O₄ at pH 6, respectively. This is attributed to the higher surface area and synergistic effect between Mn and Fe. More than 85% stability was observed with optimized catalysts employing MB and CV dyes, demonstrating the excellent reusability of the α-MnO₂-Fe₃O₄. The underlying mechanism indicates that the formation of reactive oxygen species predominantly plays a role in the photodegradation of dyes under visible light. Consequently, these new insights will shed light on the practical applications of the α-MnO₂-Fe₃O₄ 3D-flower-like spherical structure for eco-friendly remediation via wastewater treatment.

Sonochemically exfoliated polymer-carbon nanotube interface for high performance supercapacitors

Energy storage characteristics of organic molecules continue to attract attention for supercapacitor applications, as they offer simple processing and can be employed for flexible devices. The current study utilized the ultrasonically driven exfoliation to obtain poly diketo pyrrolopyrrole-thieno thiophene (PDPT) and multiwalled carbon nanotube (CNT) composite, subsequently fabricated a PDPT donor-π-acceptor heterojunction with CNT and investigated energy storage applications. The composite was characterized using series of standard analytical techniques. Morphology indicated well alighted CNT tubes on PDPT polymer nanosheets with an effective interface, providing efficient electrochemical regions, enabling fast charge transfer between PDPT and CNT. We also investigated the PDPT-CNT composite electrochemical behavior, achieving 319.2 and 105.7F.g^-1 capacitances for PDPT-CNT and PDPT at 0.5 A.g^-1 current density for three electrode configurations; and 126 and 42F.g^-1 for symmetric structures, respectively. Experimental results confirmed that PDPT-CNT composite electrodes achieved two fold the capacitance compared with PDPT alone. The hypothesis and synthetic approach provide an excellent candidate for conjugated polymers with carbon nanotubes and energy related devices.

Fabrication of Fe3O4-incorporated MnO2 nanoflowers as electrodes for enhanced asymmetric supercapacitor performance

Manganese dioxide (MnO2) is considered a promising aspirant for energy storage materials on account of its higher theoretical capacitance along with low capital cost.

Self-standing SnS nanosheet array: a bifunctional binder-free thin film catalyst for electrochemical hydrogen generation and wastewater treatment

Hydrogen generation during wastewater treatment has remained a long-standing challenge for the environment preservation welfare. In the present work, we have fabricated a promising bifunctional thin film-based catalyst for hydrogen generation with concurrent wastewater treatment. The prepared catalyst film is a vertically oriented thin SnS (tin monosulfide) nanosheet array on a Ni-foam (SnS/NF) obtained via a solution process, demonstrating a promising electrocatalytic activity towards the generation of green H₂ fuel at the cathodic side and the decomposition of urea waste at the anodic side. Notably, while assembling two identical electrodes as cathode and anode together with a reference electrode (i.e., SnS/NF∥SnS/NF vs. RHE assembly) in 1 M KOH aqueous electrolyte containing 0.33 M urea, the electrolyzer electrolyzed urea at a lower cell potential of 1.37 and 1.43 V (vs. RHE) to deliver a current density of 10 mA cm^-2 and 50 mA cm^-2, respectively, for the decomposition of urea at the anodic SnS/NF electrode and green hydrogen fuel generation at the cathodic SnS/NF electrode. This activity on electrocatalytic urea decomposition lies within the best performance to those of the previously reported sulfide-based and other catalytic materials. The promising catalytic activities of the SnS catalyst film are attributed to its combined effect of self-standing nanosheet array morphology and high crystallinity, which provides abundant active sites and a facile charge transfer path between the nanosheet arrays and the electrolyte. Thus, the present work offers a green avenue to the waste-urea treatment in water and sustainable hydrogen energy production.

A facile mechanochemical preparation of Co3O4@g-C3N4 for application in supercapacitors and degradation of pollutants in water

Our study is aimed at synthesizing cobalt oxide (Co₃O₄) with graphite carbon nitride (g-C₃N₄) to form a Co₃O₄@g-C₃N₄ hybrid through a green mechanochemical one-pot synthetic approach for manufacturing efficient supercapacitor electrodes and photocatalysts. In the present study, the Co₃O₄@g-C₃N₄ hybrid revealed a significantly higher specific capacitance (C_s) (of ~ 457.2 Fg^-1 at a current density of 1 Ag^-1) than that of the pristine Co₃O_4, which proved its pseudocapacitive behavior, with a couple of redox peaks observed in three electrode measurements (obtained by using a 3.0-M KOH aqueous electrolyte). The optimized Co₃O₄@g-C₃N₄ hybrid was further embedded for a symmetric supercapacitor performance, delivering an excellent Cs of ~ 92 Fg^-1 at a current density of 1 Ag^-1; this was supplemented with a remarkable cycling stability (~ 92% over 5000 cycles). The Co₃O₄@g-C₃N₄ hybrid was further examined for photocatalysis activity using a rhodamine B (RhB) dye, and more than 95% RhB dye was degraded through the photocatalytic reduction process (after 60 min of UV irradiation). This Co₃O₄@g-C₃N₄ hybrid catalyst exhibited excellent reusability and stability and appears to be a highly efficient, cost-effective, eco-friendly, and reusable catalyst; the g-C₃N₄ present with the Co₃O₄ acted as a conductive nano-network, leading to a higher capacitive and photocatalytic performance.

Suppressed photocatalytic activity of ZnO based Core@Shell and RCore@Shell nanostructure incorporated in the cellulose nanofiber

The protection of skin cells against intense ultra-violet (UV) rays is of greater concern and needs immediate attention. Sustainable efforts and strategies are in progress to minimize the factors that adversely affect skin cells. Herein, we synthesized zinc oxide (ZnO) in the form of core-shell (Core@Shell) or reverse core-shell (RCore@Shell) structure where silica was synthesized as a shell or core, respectively on the surface of cellulose nanofiber (CNF). Both cases exhibited much higher UV-blocking performance as well as alleviate the whitening effect because these particles retain their nanoscale dimensions as favored by the cosmetic industry. Significantly, these nanostructures shows the less photocatalysis activity than that of pristine ZnO nanoparticles. And we found that the photocatalytic activity of ZnO in RCore@Shell/CNF was more suppressed that Core@Shell/CNF, showing that it is a proper structure to neutralize or scavenge free radicals prior to their exit from the particles. Our results suggest that, reduction in photocatalysis induced by Core@Shell/CNF and RCore@Shell/CNF nanostructures is a promising strategy for skincare products in cosmetic industry.

ZIF-8 templated assembly of La3+-anchored ZnO distorted nano-hexagons as an efficient active photocatalyst for the detoxification of rhodamine B in water

The use of lanthanum-anchored zinc oxide distorted hexagon (La@ZnO DH) nanoclusters as an active material for the photodegradation of rhodamine B (Rh-B) dye via hydrogen bonding, electrostatic, and π-π interactions is examined herein. The active photocatalyst is derived from porous zeolite imidazole frameworks (ZIF-8) via a combined ultrasonication and calcination process. The distorted hexagon nanocluster morphology with controlled surface area is shown to provide excellent catalytic activity, chemical stability and demarcated pore volume. In addition, the low bandgap (3.57 eV) of La@ZnO DH is shown to expand the degradation of Rh-B under irradiation of UV light as compared to the pristine ZIF-8-derived ZnO photocatalyst due to inhibited recombination of electrons and holes. The outstanding physicochemical stability and enhanced performance of La@ZnO DH could be ascribed to the synergistic interaction among La3+ particles and the ZnO nanoclusters and provide a route for their utilization as a promising catalyst for the detoxification of Rh-B.

Highly dispersive Co3O4 nanoparticles incorporated into a cellulose nanofiber for a high-performance flexible supercapacitor

Transition metal oxides used as electrode materials for flexible supercapacitors have attracted huge attention due to their high specific capacitance and surface-to-volume ratio, specifically for cobalt oxide (Co₃O₄) nanoparticles. However, the low intrinsic electronic conductivity and aggregation of Co₃O₄ nanoparticles restrict their electrochemical performance and prevent these electrode materials from being commercialized. Herein, a facile, advantageous, and cost effective sol-gel synthetic route for growing Co₃O₄ nanoparticles uniformly over a low cost and eco-friendly one-dimensional (1D) hydrophilic cellulose nanofiber (CNF) surface has been reported. This exhibits high conductivity, which enables the symmetric electrode to deliver a high specific capacitance of ∼214 F g^-1 at 1 A g^-1 with remarkable cycling behavior (∼94% even after 5000 cycles) compared to that of pristine CNF and Co₃O₄ electrodes in an aqueous electrolyte. Furthermore, the binder-free nature of 1D Co₃O₄@CNF (which was carbonized at 200 °C for about 20 min under a H₂/Ar atmosphere) shows great potential as a hybrid flexible paper-like electrode and provides a high specific capacitance of 80 F g^-1 at 1 A g^-1 with a superior energy density of 10 W h kg^-1 in the gel electrolyte. This study provides a novel pathway, using a hydrophilic 1D CNF, for realizing the full potential of Co₃O₄ nanoparticles as advanced electrode materials for next generation flexible electronic devices.

One-Pot Synthesis of W2C/WS2 Hybrid Nanostructures for Improved Hydrogen Evolution Reactions and Supercapacitors

Tungsten sulfide (WS2) and tungsten carbide (W2C) are materialized as the auspicious candidates for various electrochemical applications, owing to their plentiful active edge sites and better conductivity. In this work, the integration of W2C and WS2 was performed by using a simple chemical reaction to form W2C/WS2 hybrid as a proficient electrode for hydrogen evolution and supercapacitors. For the first time, a W2C/WS2 hybrid was engaged as a supercapacitor electrode and explored an incredible specific capacitance of ~1018 F g-1 at 1 A g-1 with the outstanding robustness. Furthermore, the constructed symmetric supercapacitor using W2C/WS2 possessed an energy density of 45.5 Wh kg-1 at 0.5 kW kg-1 power density. For hydrogen evolution, the W2C/WS2 hybrid produced the low overpotentials of 133 and 105 mV at 10 mA cm-2 with the small Tafel slopes of 70 and 84 mV dec-1 in acidic and alkaline media, respectively, proving their outstanding interfaced electrocatalytic characteristics. The engineered W2C/WS2-based electrode offered the high-performance for electrochemical energy applications.

1D-CoSe2 nanoarray: a designed structure for efficient hydrogen evolution and symmetric supercapacitor characteristics

Direct growth of self-supported one-dimensional (1D) nanorod arrays on conducting substrates is highly attractive for electrocatalysis, due to their unique shape, size, and length.