Tunable Catalytic Activity Research Articles

3D printed triboelectric nanogenerator self-powered electro-Fenton degradation of orange IV and crystal violet system using N-doped biomass carbon catalyst with tunable catalytic activity

Self-powered electro-Fenton (EF) degradation systems based on triboelectric nanogenerator (TENG) technology supply one constructive approach for organic pollution degradation in energy-saving and environmental-friendly manners. Herein, a novel self-powered EF degradation system was built via combining 3D printed flexible multilayered triboelectric nanogenerator (PFM-TENG) with the N-doped porous carbon materials as EF cathode catalysts. The PFM-TENG has a simple multilayered structure but high output characteristics that Voc, Isc, Qtr, Pdensity are 450.0 V, 1.9 mA, 2.9 μC, and 5.1 W m−2, respectively. Besides, the as-prepared cathode carbon materials feature a high surface area of 1790.8 m2 g−1, the total doping content of N, O is up to 20.6 at.%. Driven by PFM-TENG, the EF degradation efficiencies of orange Ⅳ and crystal violet are up to 96.0% and 95.4% in 60 min, respectively. It is noteworthy that there is a positive correlation between the content of –C–O–C functional groups and the degradation efficiency through the analysis of the structure-activity relationship of the carbon materials catalysts. This work realizes the high-efficiency degradation of orange IV and crystal violet through the combination of N-doped carbon catalyst design and 3D printed triboelectric nanogenerator, which not only provides ideas for the preparation of N-doped carbon catalytic materials with controllable catalytic activity, but also proposes an innovative scheme for the layout of the future-oriented EF degradation systems and even the other electrochemical systems via self-powered, digital, mass-produced, distributed, and environmental manners.

Rationalization of promoted reverse water gas shift reaction by Pt3Ni alloy: Essential contribution from ensemble effect.

Bimetallic alloys have attracted considerable attention due to the tunable catalytic activity and selectivity that can be different from those of pure metals. Here, we study the superior catalytic behaviors of the Pt3Ni nanowire (NW) over each individual, Pt and Ni NWs during the reverse Water Gas Shift (rWGS) reaction, using density functional theory. The results show that the promoted rWGS activity by Pt3Ni strongly depends on the ensemble effect (a particular arrangement of active sites introduced by alloying), while the contributions from ligand and strain effects, which are of great importance in electrocatalysis, are rather subtle. As a result, a unique Ni-Pt hybrid ensemble is observed at the 110/111 edge of the Pt3Ni NW, where the synergy between Ni and Pt sites is active enough to stabilize carbon dioxide on the surface readily for the rWGS reaction but moderate enough to allow for the facile removal of carbon monoxide and hydrogenation of hydroxyl species. Our study highlights the importance of the ensemble effect in heterogeneous catalysis of metal alloys, enabling selective binding-tuning and promotion of catalytic activity.

Rational Manipulation of Stacking Arrangements in Three-Dimensional Zeolites Built from Two-Dimensional Zeolitic Nanosheets.

Unit-cell-thin zeolitic nanosheets have emerged as fascinating materials for catalysis and separation. The controllability of nanosheet stacking is extremely challenging in the chemistry of two-dimensional zeolitic materials. To date, the organization of zeolitic nanosheets in hydrothermal synthesis has been limited by the lack of tunable control over the guest-host interactions between organic structure-directing agents (OSDAs) and zeolitic nanosheets. A direct synthetic methodology is reported that enables systematic manipulation of the aluminosilicate MWW-type nanosheet stacking. Variable control of guest-host interactions is rationally achieved by synergistically altering the charge density of OSDAs and synthetic silica-to-alumina composition. These finely controlled interactions allow successful preparation of a series of three-dimensional (3D) zeolites, with MWW-layer stacking in wide ranges from variably disorder to fully ordered, leading to tunable catalytic activity in the cracking reaction. These results highlight unprecedented opportunities to modulate zeolitic nanosheets arrangement in 3D zeolites whose structure can be tailored for catalysis and separation.

Rational Manipulation of Stacking Arrangements in Three‐Dimensional Zeolites Built from Two‐Dimensional Zeolitic Nanosheets

AbstractUnit‐cell‐thin zeolitic nanosheets have emerged as fascinating materials for catalysis and separation. The controllability of nanosheet stacking is extremely challenging in the chemistry of two‐dimensional zeolitic materials. To date, the organization of zeolitic nanosheets in hydrothermal synthesis has been limited by the lack of tunable control over the guest–host interactions between organic structure‐directing agents (OSDAs) and zeolitic nanosheets. A direct synthetic methodology is reported that enables systematic manipulation of the aluminosilicate MWW‐type nanosheet stacking. Variable control of guest–host interactions is rationally achieved by synergistically altering the charge density of OSDAs and synthetic silica‐to‐alumina composition. These finely controlled interactions allow successful preparation of a series of three‐dimensional (3D) zeolites, with MWW‐layer stacking in wide ranges from variably disorder to fully ordered, leading to tunable catalytic activity in the cracking reaction. These results highlight unprecedented opportunities to modulate zeolitic nanosheets arrangement in 3D zeolites whose structure can be tailored for catalysis and separation.

Iron Phthalocyanine/Graphene Composites as Promising Electrocatalysts for the Oxygen Reduction Reaction

Recently, the development of non-precious electrocatalysts for the oxygen reduction reaction (ORR) has become important in replacing currently employed platinum (Pt)-based catalysts. Although Pt-based catalysts exhibit satisfactory ORR performances, their high price, easy methanol/CO2 poisoning, and poor long-term stability significantly hamper the forward movement of fuel cell technology. Among the various candidates, graphene-supported iron phthalocyanine (FePc) composites have attracted great attention because of their unique advantages, including low cost, good dimensional stability, high durability, and tunable catalytic activity. In the composite catalyst, FePc molecules are immobilized on graphene via noncovalent or covalent interactions. In addition, two-dimensional graphene substrates can improve not only the electrical conductivity of the composite, but also the dispersion of FePc molecules, triggering a significant improvement in the catalytic properties of the composite catalyst. Herein, we summarize the recent advances in FePc/graphene composite catalysts used for the ORR. Moreover, we discuss the challenges and future perspectives of this promising field.

Tunable catalytic activity of gadolinium-doped ceria nanoparticles for pro-oxidation of hydrogen peroxide

We report a study of the roles of gadolinium(III) (Gd3+) dopants in influencing the catalytic activity of gadolinium-doped ceria nanoparticles towards the pro-oxidation of hydrogen peroxide to hydroxyl radicals. These doped ceria nanoparticles with dopant concentrations of 0.6 wt.%, 3 wt.%, and 6 wt.% Gd3+ were synthesized using an ozone-mediated method for tuning their catalytic activities. The Gd dopants were found to foster an increase in the percentage of Ce3+ ions in the doped ceria nanoparticles. Our reaction kinetic study revealed that the relationship between the overall reaction rates and the Gd dopant concentrations in our doped materials followed a volcano-like trend. In contrast, the apparent activation energy values of these Gd-doped ceria nanoparticles were found to be positively associated with the concentrations of Gd dopants. The overall catalytic activity trend was attributed to the interplay between the promotion and degradation effects of the Gd dopants on the properties of doped ceria nanoparticles.

Amphiphilic poly(ionic liquid)/Wells–Dawson‐type phosphovanadomolybdate ionic composites as efficient and recyclable catalysts for the direct hydroxylation of benzene with H2O2

Three novel amphiphilic poly(ionic liquid) (PIL)/Wells–Dawson‐type phosphovanadomolybdate (V‐POM) ionic composites with tunable oxidative catalytic activity and unique nanostructure were synthesized using carboxylic acid‐functionalized PIL and H7[P2Mo17VO62], H8[P2Mo16V2O62] and H9[P2Mo15V3O62] as synthetic units via self‐assembly in water. The results of characterization indicated that V‐POM anions were finely dispersed in the PIL cation framework, and their structures were well preserved. The three composites are amorphous V‐POM salts of PIL cation with a considerable thermal stability, and an open three‐dimensional network structure with hierarchical porosity. The as‐synthesized composites were found to be efficient heterogeneous catalysts for the direct hydroxylation of benzene to phenol with H2O2 in the liquid phase. Under optimum conditions, a phenol yield of 37.3% was achieved with selectivity of 100%. The high catalytic performance could be attributed to the synergistic catalytic effect between V‐POM anion and carboxylic acid‐functionalized PIL cation framework, and good benzene adsorption and phenol desorption ability of amphiphilic micropores in the structure of the composites. Additionally, these composites exhibited high stability under the reaction conditions and could be easily recovered and reused at least six times without noticeably loss of activity.

Tunable catalytic activity of gold nanoparticle decorated SBA-15/PDMAEMA hybrid system

A temperature responsive smart catalytic system based on SBA-15/poly(N,N-dimethylaminoethylmethacrylate) decorated with gold nanoparticles (NPs) was prepared. The surface graft polymerization of 2-dimethylaminoethyl methacrylate on well-structured mesoporous silica NPs was done by atom transfer radical polymerization technique in aqueous alcohol media. In situ generation of gold NPs was achieved in controlled condition. The catalytic activity was evaluated by monitoring the reduction reaction of 4-nitrophenol at various temperatures. The catalytic activity of the NPs showed a deviance from the expected Arrhenius trend at different temperatures. Above the cloud point of the grafted polymer at a given pH condition, the rate constant of the catalytic reaction dropped sharply due to shrinkage of the polymer and transition to hydrophobic state.

Porous manganese-cobalt oxide microspheres with tunable oxidase mimicking activity for sulfide ion colorimetric detection.

Here, we report the controllable synthesis of porous MnxCo1-xO microspheres and tunable catalytic activity in the oxidase mimicking reaction. Mn0.6Co0.4O possesses the best oxidase mimicking activity and can be used successfully in sulfide ion colorimetric detection with a low detection limit of 0.1 μM.

Poly(N-isopropylacrylamide)@graphene oxide-Ag responsive hydrogels. Characterization and smart tunable catalytic activity

Thermally responsive hydrogels have drawn significant research attention recently because of their simple use as smart catalyst. Here we design a series of responsive hydrogels that incorporate graphene oxide (GO)-Ag composites into thermo-responsive N-isopropylacrylamide (NIPAM) at different mass ratios. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and UV-visible absorption spectroscopy. Meanwhile, the PNIPAM/GO-Ag hydrogels showed high catalytic activity in the hydrogenation reaction of nitrophenol to aminophenol and acted as a tunable catalyst which the swelling and collapsing could be triggered by small temperature changes around the lower critical solution temperature (LCST) of the hydrogels. The present approach can shed new light on designing of catalytic material like GO-Ag composite responsive hydrogel with promising applications in catalysis.

Tunable catalytic activity of cobalt-intercalated layered MnO2 for water oxidation through confinement and local ordering

The lowering of reaction overpotentials is a persistent and universal goal in the development of catalysts for (photo)electrochemistry, which can usually be facilitated by selectively stabilizing one reaction intermediate over another. In this mechanistic study of the oxygen evolution reaction (OER) catalyzed by cobalt-intercalated layered MnO2, we show that confinement effects and local cobalt atomic ordering in the interlayer space can be synergistically used to tune the adsorption energies of O, OH, and OOH reaction intermediates and the scaling relationship between them. In general, the interlayer confinement destabilizes the adsorption of intermediates for the OER, but clustering Co atoms can selectively stabilize the adsorption of OOH in particular. After considering both effects, our model predicts an overpotential of 0.30 V for the Co-intercalated MnO2 catalyzed OER, in excellent agreement with the experimental result of 0.36 V. These new insights explain the enhanced catalytic performance of MnO2 by intercalating atoms and illuminate a route for engineering non-toxic precious-metal-free catalysts through designed layered materials.

Peroxidase-Like Activity of Smart Nanomaterials and Their Advanced Application in Colorimetric Glucose Biosensors.

Diabetes is a dominating health issue with 425 million people suffering from the disease worldwide and 4 million deaths each year. To avoid further complications, the diabetic patient blood glucose level should be strictly monitored despite there being no cure for diabetes. Colorimetric biosensing has attracted significant attention because of its low cost, simplicity, and practicality. Recently, some nanomaterials have been found that possess unexpected peroxidase-like activity, and great advances have been made in fabricating colorimetric glucose biosensors based on the peroxidase-like activity of these nanomaterials using glucose oxidase. Compared with natural horseradish peroxidase, the nanomaterials exhibit flexibility in structure design and composition, and have easy separation and storage, high stability, simple preparation, and tunable catalytic activity. To highlight the significant progress in the field of nanomaterial-based peroxidase-like activity, this work discusses the various smart nanomaterials that mimic horseradish peroxidase and its mechanism and development history, and the applications in colorimetric glucose biosensors. Different approaches for tunable peroxidase-like activity of nanomaterials are summarized, such as size, morphology, and shape; surface modification and coating; and metal doping and alloy. Finally, the conclusion and challenges facing peroxidase-like activity of nanomaterials and future directions are discussed.

Tunable catalytic activities of different α-Fe2O3 surface areas in ammonium perchlorate thermal decomposition

Different surface areas of α-Fe2O3 nanocrystals have been achieved by annealing at different temperatures. Obtained samples were characterized by X-ray diffraction, Brunauer–Emmett–Teller technique, and transmission electron microscopy. The surface areas of α-Fe2O3 nanocrystals changed from 136.5 m2/g to 2.1 m2/g with the increase of annealing temperature from 280 °C to 700 °C. α-Fe2O3 nanocrystal catalytic activity on the decomposition of ammonium perchlorate (AP) was characterized through thermogravimetric analysis. The decomposition rate of AP with the addition of α-Fe2O3 nanocrystals was surface area relative. The 136.5 m2/g α-Fe2O3 nanocrystal exhibited the best catalytic activity, which lowered the high-temperature peak temperature of AP by 60.8 °C.

Biophysical characterization of a recombinant lipase KV1 from Acinetobacter haemolyticus in relation to pH and temperature

Spectroscopic and calorimetric methods were employed to assess the stability and the folding aspect of a novel recombinant alkaline-stable lipase KV1 from Acinetobacter haemolyticus under varying pH and temperature. Data on far ultraviolet-circular dichroism of recombinant lipase KV1 under two alkaline conditions (pH 8.0 and 12.0) at 40 °C reveal strong negative ellipticities at 208, 217, 222 nm, implying its secondary structure belonging to a α + β class with 47.3 and 39.0% ellipticity, respectively. Results demonstrate that lipase KV1 adopts its most stable conformation at pH 8.0 and 40 °C. Conversely, the protein assumes a random coil structure at pH 4.0 and 80 °C, evident from a strong negative peak at ∼ 200 nm. This blue shift suggests a general decline in enzyme activity in conjunction with the partially or fully unfolded state that invariably exposed more hydrophobic surfaces of the lipase protein. The maximum emission at ∼335 nm for pH 8.0 and 40 °C indicates the adoption of a favorable protein conformation with a high number of buried tryptophan residues, reducing solvent exposure. Appearance of an intense Amide I absorption band at pH 8.0 corroborates an intact secondary structure. A lower enthalpy value for pH 4.0 over pH 8.0 and 12.0 in the differential scanning calorimetric data corroborates the stability of the lipase at alkaline conditions, while a low Km (0.68 ± 0.03 mM) for tributyrin verifies the high affinity of lipase KV1 for the substrate. The data, herein offer useful insights into future structure-based tunable catalytic activity of lipase KV1.

Tailored Macroporous Hydrogels with Nanoparticles Display Enhanced and Tunable Catalytic Activity.

This work demonstrates that a model system of poly( N-isopropylacrylamide) (PNIPAam) macroporous hydrogels, with tailored microstructures and comprising gold (Au) or silver (Ag) nanoparticles, display enhanced and tunable catalytic activity. These nanocomposites are prepared using polymer templates obtained from melt-processed cocontinuous polymer blends. The reaction rate, controlled by both hydrogel porosity and the PNIPAam lower critical solution temperature, increases by more than an order of magnitude as compared to nonporous gels, and is comparable to micro- or nanocarrier-based systems, with easier catalyst recovery. The fabrication process is scalable, and is compatible with broad choices of polymer blend, gel, and nanoparticle chemistries.

(Invited) Nanoporous Materials for Energy and Environmental Applications

Bicontinuous nanoporous materials are emerging as a new class of functional materials because of a large surface area, high porosity and mechanical rigidity which traditional porous materials, such as metal foams, do not have. Coupled with excellent electric conductivity and rich surface chemistry, the nanoporous materials show great promises for energy and environment related applications. In this presentation I will introduce our recent works in the development of nanoporous metallic compounds by selective phase dissolution and nanoporous two-dimensional materials (graphene, MoS2, etc) by nanoporous metal based chemical vapor deposition. These novel nanoporous materials with tunable electronic structure and catalytic activities have been successfully employed as the catalytic electrodes for electrochemical and photoelectrochemical hydrogen productions, solar energy conversion, and Li-O2 batteries.

Tunable Bifunctional Activity of Mnx Co3-x O4 Nanocrystals Decorated on Carbon Nanotubes for Oxygen Electrocatalysis.

Noble‐metal‐free electrocatalysts are attractive for cathodic oxygen catalysis in alkaline membrane fuel cells, metal–air batteries, and electrolyzers. However, much of the structure–activity relationship is poorly understood. Herein, the comprehensive development of manganese cobalt oxide/nitrogen‐doped multiwalled carbon nanotube hybrids (MnxCo3−xO4@NCNTs) is reported for highly reversible oxygen reduction and evolution reactions (ORR and OER, respectively). The hybrid structures are rationally designed by fine control of surface chemistry and synthesis conditions, including tuning of functional groups at surfaces, congruent growth of nanocrystals with controllable phases and particle sizes, and ensuring strong coupling across catalyst–support interfaces. Electrochemical tests reveal distinctly different oxygen catalytic activities among the hybrids, MnxCo3−xO4@NCNTs. Nanocrystalline MnCo2O4@NCNTs (MCO@NCNTs) hybrids show superior ORR activity, with a favorable potential to reach 3 mA cm−2 and a high current density response, equivalent to that of the commercial Pt/C standard. Moreover, the hybrid structure exhibits tunable and durable catalytic activities for both ORR and OER, with a lowest overall potential of 0.93 V. It is clear that the long‐term electrochemical activities can be ensured by rational design of hybrid structures from the nanoscale.

Enzyme Mimicry for Combating Bacteria and Biofilms.

Bacterial infection continues to be a growing global health problem with the most widely accepted treatment paradigms restricted to antibiotics. However, antibiotics overuse and misuse have triggered increased multidrug resistance, frustrating the therapeutic outcomes and leading to higher mortalities. Even worse, the tendency of bacteria to form biofilms on living and nonliving surfaces further increases the difficulty in confronting bacteria because the extracellular matrix can act as a robust barrier to prevent the penetration of antibiotics and resist environmental stress. As a result, the inability to completely eliminate bacteria and biofilms often leads to persistent infection, implant failure, and device damage. Therefore, it is of paramount importance to develop alternative antimicrobial agents while avoiding the generation of bacterial resistance. Taking lessons from natural enzymes for destroying cellular structural integrity or interfering with metabolisms such as proliferation, quorum sensing, and programmed death, the construction of artificial enzymes to mimic the enzyme functions will provide unprecedented opportunities for combating bacteria. Moreover, compared to natural enzymes, artificial enzymes possess much higher stability against stringent conditions, easier tunable catalytic activity, and large-scale production for practical use. In this Account, we will focus on our recent progress in the design and synthesis of artificial enzymes as a new generation of "antibiotics", which have been demonstrated as promising applications in planktonic bacteria inactivation, wound/lung disinfection, as well as biofilm inhibition and dispersion. First, we will introduce direct utilization of the intrinsic catalytic activities of artificial enzymes without dangerous chemical auxiliaries for killing bacteria under mild conditions. Second, to avoid the toxicity caused by overdose of H2O2 in conventional disinfections, we leveraged artificial enzymes with peroxidase-mimic activities to catalyze the generation of hydroxyl radicals at low H2O2 levels while achieving efficient antibacterial outcomes. Importantly, the feasibility of these artificial enzymes was further demonstrated in vivo by mitigating mice wound and lung disinfection. Third, by combining artificial enzymes with stimuli-responsive materials, smart on-demand therapeutic modalities were constructed for thwarting bacteria in a controllable manner. For instance, a photoswitchable "Band-Aid"-like hydrogel doped with artificial enzymes was developed for efficiently killing bacteria without compromising mammal cell proliferation, which was promising for accelerating wound healing. Lastly, regarding the key roles that extracellular DNAs (eDNAs) play in maintaining biofilm integrity, we further designed a multinuclear metal complex-based DNase-mimetic artificial enzyme toward cleaving the eDNA for inhibiting biofilm formation and dispersing the established biofilms. We expect that our rational designs would boost the development of artificial enzymes with different formulations as novel antibacterial agents for clinical and industrial applications.

Molybdenum carbide nanoparticle decorated hierarchical tubular carbon superstructures with vertical nanosheet arrays for efficient hydrogen evolution

With Mo2C nanoparticle decorated carbon tube-sheet superstructures, Mo2C/CTSSs manifest tunable catalytic activity towards hydrogen evolution reaction by changing the arrangement of carbon nanosheet arrays.

Hierarchical CNFs/MnCo2O4.5 nanofibers as a highly active oxidase mimetic and its application in biosensing

Recently, much attention has been paid on the nanomaterial-based artificial enzymes due to their tunable catalytic activity, high stability and low cost compared to the natural enzymes. Different from the peroxidase mimics which have been studied for several decades, nanomaterials with oxidase-like property are burgeoning in the recent years. In this paper, hierarchical carbon nanofibers (CNFs)/MnCo2O4.5 nanofibers as efficient oxidase mimics are reported. The products are synthesized by an electrospinning technique and an electrochemcial deposition process in which the CNFs are used as the working electrode where MnCo2O4.5 nanosheets deposit on. The resulting binary metal oxide-based nanocomposites exhibit a good oxidase-like activity toward the oxidations of 3,3′,5,5′tetramethylbenzi-dine (TMB), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium (ABTS) salt and o-phenylenediamine (OPD) without exogenous addition of H2O2. The system of CNFs/MnCo2O4.5-TMB can be used as a candidate to detect sulfite and ascorbic acid via a colorimetric method with a high sensitivity. This work provides the efficient utilization and potential applications of binary metal oxide-based nanocomposites with oxidase activities in biosensors and other biotechnologies.