Macropore Arrays Research Articles

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling

AbstractCatalytic upcycling of polyolefins into high‐value chemicals represents the direction in end‐of‐life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM‐5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre‐cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1‐C7) are produced with a yield of 443 mmol gZSM‐5−1, where 74.3 % of them are C3‐C6 olefins, much superior to ZSM‐5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling.

Catalytic upcycling of polyolefins into high-value chemicals represents the direction in end-of-life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM-5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre-cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1-C7) are produced with a yield of 443 mmol gZSM-5 -1, where 74.3 % of them are C3-C6 olefins, much superior to ZSM-5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Fabrication of Ordered Macropore Arrays in n-Type Silicon Wafer by Anodic Etching Using Double-Tank Electrochemical Cell.

In this work, ordered macropore arrays in n-type silicon wafers were fabricated by anodic etching using a double-tank electrochemical cell. The effects of the wafer thickness, etching time and voltage on the quality of macropore arrays were investigated. Homogeneous macropore arrays could be achieved in 200 μm thick silicon wafers, but could not be obtained from 300 and 400 μm thick silicon wafers. Highly ordered macropore arrays with an aspect ratio of 19 were fabricated in 200 μm thick n-type silicon at 4.5 V. The etching current decreases in 200 μm thick silicon but increases in thicker silicon with an increase in time. It demonstrates that the minority carrier transportation capability from the illuminated surface to the reactive surface is different for silicon wafers with different thicknesses. The minority carrier concentration at the illuminated surface for stable macropore formation and the current under different etching voltages were calculated based on a hole transport model. The results show that appropriately decreasing wafer thickness and increasing voltage can help stable macropore array fabrication in the illumination-limited double-tank cell.

A photoactivated gas sensor of SnO2 ordered spherical pore array: Electrodeposition-based construction and application in room temperature detection of ethanol gas

The photoactivated semiconductor film gas sensor has received increasing attention in the room temperature detection of environmental gases, but the uncontrolled surface morphology and the associated light area still limit the application and the exploitation of the sensing response potential. Herein, a monolayer colloid crystal template strategy based on electrodeposition was introduced to in situ construct SnO2 ordered spherical macropore array (OSPA) sensors used for ethanol gas detection under a UV-LED. By adjusting the electrodeposition time, various OSPAs with regularly variable heights of pore-wall were obtained. The light area of the array could then be systematically regulated based on the spherical pore-walls’ curve characteristics. The OSPAs showed a nearly 5-fold change in response in detection of 100 ppm ethanol gas under a 265 nm UV-LED, corresponding to the light area from small to large. The highest sensing response is even higher than that of almost all SnO2-based room temperature sensors that have previously been reported. Moreover, the sensor has excellent selectivity and linearity, a 1 ppm lower detection limit, and exceptional long-term stability. These finds are corroborated by analyses of the electrodeposition mechanism, the sensing mechanism, optical simulations, and various characterizations. The strategy provides an efficient way to tune and enhance the sensing response of a photoactivated gas sensor, and is beneficial for exploiting the sensing potential of a semiconductor.

Ge-on-insulator fabrication based on Ge-on-nothing technology

Ge-on-Insulator (GOI) is considered to be a necessary structure for novel Ge-based devices. This paper proposes an alternative approach for fabricating GOI based on the Ge-on-Nothing (GeON) template. In this approach, a regular macropore array is formed by lithography and dry etching. These pores close and merge upon annealing, forming a suspended monocrystalline Ge membrane on one buried void. GOI is fabricated by direct bonding of GeON on Si carrier substrates, using an oxide bonding interface, and subsequent detachment. The fabricated GOI shows uniform physical properties as demonstrated using micro-photoluminescence measurements. Its electrical characteristics and cross-sectional structure are superior to those of Smart-CutTM GOI. To demonstrate its application potential, back-gate GOI capacitors and MOSFETs are fabricated. Their characteristics nicely agree with the theoretically calculated one and show typical MOSFET operations, respectively, which indicates promising Ge crystallinity. This method, therefore, shows the potential to provide high-quality GOI for advanced Ge application devices.

Boosting redox kinetics using rationally engineered cathodic interlayers comprising porous rGO–CNT framework microspheres with NiSe2-core@N-doped graphitic carbon shell nanocrystals for stable Li–S batteries

Here, we propose the synthesis of a three-dimensional (3D) nanostructure comprising NiSe2-core@N–doped graphitic carbon (NGC) shell nanocrystals securely implanted within a highly conductive and porous reduced graphene oxide–carbon nanotube (rGO–CNT) framework (3D P-NiSe2@NGC/rGO–CNT), using spray pyrolysis technique followed by selenization and utilized as multifunctional cathodic interlayers in lithium–sulfur (Li–S) cells. The uniformly distributed arrays of macropores (ϕ = 100 nm) were formed by thermal decomposition of polystyrene nanobeads (ϕ = 200 nm). The porous structure shortens the charge diffusion length, allowing rapid charge transport and efficient electrolyte percolation besides accommodating unwanted volume perturbations. The NGC shell surrounding the NiSe2 nanocrystals acted as the primary conduction conduit for electron transport, while the self-supporting rGO–CNT framework served as a secondary pathway for consecutive electron transfer besides enhancing the structural robustness. Further, the polar NiSe2 nanocrystals offered numerous chemisorption sites for effectively capturing polysulfides, thus minimizing the shuttling effect and increasing active material utilization. The Li–S cell exhibited improved rate performance (till 4.0C) and excellent cycling stability (1000 cycles at 2.0C, average capacity decay rate of 0.04% per cycle). Even at severe cell parameters (effective S content = 74%, S loading = 4.5 mg cm−2, and electrolyte/sulfur = 5.7 µL mg−1), the cells delivered a stable rate performance and long-term cycling (400 cycles at 0.1C, average decay rate of 0.10% per cycle). We believe the nanostructure design strategy that we developed for this study could spur the development of more enduring and practical Li–S battery technology.

Corrosion engineering towards NiFe-layered double hydroxide macroporous arrays with enhanced activity and stability for oxygen evolution reaction.

NiFe-layered double hydroxide (NiFe-LDH) is the benchmark catalyst for the oxygen evolution reaction (OER) in alkaline medium, however, it is still challenging to improve its activity and stability. Herein, NiFe-LDH macroporous array electrodes are demonstrated to significantly enhance the activity and stability for oxygen evolution reaction. The electrodes are fabricated by the chemical and electrochemical corrosion process of Ni foam induced by ferric nitrate, hydrochloric acid and oxygen. are prepared by a controllable corrosion strategy for oxygen evolution reaction. By optimizing the amount of iron salt and acid and selecting the appropriate reaction temperature and time, The NiFe-LDH electrodes only need the overpotential of 180 mV and 248 mV to reach the current density of 10 mA cm-2 and 500 mA cm-2, respectively, and remain highly stable for 1000 h at 500 mA cm-2. The unique macroporous array not only significantly increases the active area of NiFe-LDH catalyst, but also creates a stable nanostructure that avoids severe reconstruction.

In situ self-assembled macroporous interconnected nanosheet arrays of Ni-1,3,5-benzenetricarboxylate metal − organic framework on Ti mesh as high-performance oxygen evolution electrodes

Highly efficient metal–organic framework (MOF)-based oxygen evolution reaction (OER) catalysts are desirable for water splitting, but their development remains challenging due to poor accessibility of coordinatively unsaturated metal (cum) sites and low intrinsic activity. A large-area three-dimensional (3-D) macroporous interconnected nanosheet array of Ni-1,3,5-benzenetricarboxylate has been in situ self-assembled on Ti mesh (TM) by using ethanol as the solvent and high-affinity oxide layer on TM to promote in situ nucleation. The obtained nanoarchitecture exhibits much superior catalytic activity compared to most reported catalysts including MOF-based catalysts, other precious-metal-free ones, and Ir/Ru-based ones. Additionally, this electrode undergoes no current decay after 300 cyclic voltammetry (CV) cycles and can maintain at 250 mA cm−2 for over 266 h. The excellent catalytic performance is mainly due to the 3-D macroporous and interconnected nanosheet array structure improving cum site exposure and charge transport and in situ activated cum cations enhancing OH− adsorption. This work not only develops a facile and economical approach to synthesize 3-D macroporous interconnected MOF nanosheet arrays to simultaneously increase the number, exposure, and intrinsic activity of active sites and facilitate charge transport for high-performance eletrocatalysis, but provides scientific insights into the mechanisms for self-assembly of this unique nanoarchitecture and for the high OER performance.

Rotary-angle 3D printing multilayer membrane dead-end filtration for rapid and highly efficient water treatment

Polluted water caused by antibiotics leads to serious risks to human health and ecosystem. Rapidly and efficiently treating antibiotic pollutions to make it safe is urgently needed for environmental protection and public health. Herein, we report that ZIF-67 derived nano-cube Co3O4 as model catalysts were immobilized in the rotary-angle three-dimensional (3D) printed multilayer reduced graphene oxide/carbon nanotubes (Co3O4/R-rGO/CNTs) membrane for the highly efficient degradation of antibiotic pollutants through sulfate radical-based advanced oxidation process (SR-AOP). The macropores in the designed Co3O4/R-rGO/CNTs membrane are distributed in a rotationally staggered arrangement, which increases the opportunity for contaminant contact with the catalyst. The micro-cellular structures formed by the freeze-casting treatment in Co3O4/R-rGO/CNTs membrane provide abundant anchor sites for catalysts as-well-as plentiful active sites for catalytic reactions. The degradation efficiency of the designed membrane toward aureomycin hydrochloride (CTC) reached 99.3% at a flux rate of 636.9 L m−2 h−1, which is increased by 100% comparing with the traditional 3D printing membrane with vertical macroporous arrays. This strategy put forward a new idea for the efficient degradation of antibiotic pollutants and has great application prospects in the field of environmental remediation.

Fabrication of P(100) silicon macro-pore and pillar array by wet electrochemical etching

In this paper, pyramidal notch array was pre-etched on P(100) silicon wafer using anisotropic wet chemical etching, then macro-pore/pillar array were successfully processed in the pyramidal notch array by an anodic electrochemical etching. The formation mechanism of macro-pore and pillar in pyramidal notch were investigated, it indicates that the silicon dissolution rate is proportional to electric field, while electric field is mainly concentrated on the tip, edges and corners of the pyramidal notch. Therefore, there is an etching rate difference between the notch corner and planar regions in the pyramid notch. The notch corners are preferentially etched at first, then a pore is formed in the notch. If the shape of the open window is truncated and the bottom size is large enough, four pores would initiate at the notch angels due to etching rate difference between the truncated pyramidal notch corner and notch center, consequently, a pillar is formed in the notch center.

A Three-Dimensional Activated Carbon Electrode with Carbon Fiber Felt Framework and Ordered Macropores for Enhanced Capacitive Deionization Performance

Capacitive deionization (CDI) is a promising energy-efficient electrochemical water treatment technology and a scalable electrode having high mass loading is an essential imperative to the success of this technology. A thick CDI electrode was constructed by loading activated carbon particles as the electroactive material into a three-dimensional framework fabricated from a mixture felt of conductive carbon fiber serving as an electron transfer channel and removable yak hair functioning to provide an ion transport pathway. The carbon fiber reduces the electrode electrical resistance and the ultimately removed yak hair creates an ordered macropore array that provides an ion reservoir as well as a conduction channel for reducing ion transport distance inside the electrode. The resulting composite electrode with an optimal carbon fiber and yak hair content shows a specific capacitance of 219.27 F g-1 at 0.1 A g-1 and reaches salt adsorption capacity of 15.75 mg g-1 and average salt adsorption rate of 17.10 mg g-1 h-1 with more than 50% retention after 200 cycles. The designed three-dimensional composite exhibits enhanced deionization and long-term stability that is believed to be a low-cost and simple assembly solution for achieving a high mass loading and scalable electrode for the industrial CDI applications.

Macroporous Array Induced Multiscale Modulation at the Surface/Interface of Co(OH)2/NiMo Self‐Supporting Electrode for Effective Overall Water Splitting

AbstractOutstanding electrocatalysts for high‐efficiency water splitting demand not only the high intrinsic activity determined by the electronic structure but also a favorable mass transfer (electrolyte diffusion and bubble desorption) and strong structural stability. Here, a 3D core–shell electrocatalyst consisting of Co(OH)2 cavity array‐encapsulated NiMo alloy on the flexible carbon cloth substrate (Co(OH)2/NiMo CA@CC) is proposed. Density functional theory reveals that coupling NiMo with Co(OH)2 can better optimize the water adsorption/dissociation and hydrogen adsorption energies in hydrogen evolution reaction, and also accelerate the kinetics of oxygen evolution reaction. Based on this, the open porous structure of the outer Co(OH)2 cavity array further promotes the diffusion of the electrolyte into the heterogeneous interface between NiMo and Co(OH)2, significantly shortening the electron transfer pathways and exposing multiple active sites. In addition, the macroporous array structure accelerates the bubble evolution and desorption process, thus ensuring a rapid mass transfer. When served as bifunctional electrocatalysts toward alkaline overall water splitting, Co(OH)2/NiMo CA@CC delivers a current density of 10 mA cm−2 at a low cell voltage of 1.52 V. Results support the multiscale optimization of the surface/interface engineering induced by the macroporous array.

Amphiphilic ionic liquid assembly route for the synthesis of polymer/Ag spheres and Ag-decorated bimodal porous silica

The multifunctional assembly of amphiphilic ionic liquids (AILs) can play an important role in the synthesis of various composite nanomaterials. In this work, we developed a novel strategy to steer the generation of polymer/AIL16/Ag spheres by using amphiphilic ionic liquid, 1-hexadecyl-3-methylimidazolium chloride (AIL16) as a “bridge”. Two kinds of polymer spheres (poly(methyl methacrylate), PMMA or polystyrene, PS) were used to assemble of the PMMA/AIL16/Ag (or PS/AIL16/Ag) microspheres. Subsequently, the PMMA/AIL16/Ag (or PS/AIL16/Ag) microspheres and AIL16 were used as templating agents of macropores and mesoporores respectively to prepare Ag-decorated bimodal porous silica. The effects of mass ratios of m(Ag)/m(PMMA, or PS) and amount of AIL16 on the formation of the PMMA (or PS)/AIL16/Ag microspheres and the Ag-decorated bimodal porous silica structure were investigated in detail. It was found that the dispersity and loading capacity of Ag nanoparticles onto the polymer spheres and the structures of the bimodal porous silica can be easily manipulated by changing the mass ratios of m(Ag)/m(PMMA, or PS) and the amount of adding AIL16. The obtained Ag-decorated bimodal porous silica exhibited three dimensional ordered spherical macroporous array with an ordered mesoporous silica walls, in which Ag-NPs with good dispersibility were immobilized onto the inner walls of the macroporous holes. Furthermore, the synthesized Ag-decorated bimodal porous silica displayed a better catalytic activity for the reduction reaction of 4-nitrophenol by using NaBH4 as reducer.

Template-directed preparation of three-dimensionally ordered macroporous molecularly imprinted microspheres for selective recognition and separation of quinine from cinchona extract

A kind of novel three-dimensionally ordered macroporous molecularly imprinted microspheres (3DMIMs) had been developed for selective recognition and separation of quinine based on the combination of colloidal crystal templating method and molecular imprinting technique. The 3DMIMs were derived from the spherical silica colloidal crystal involving a four-step templating process including infiltration of imprinted precursors, sealing of polyethylene glycol, initiation polymerization, as well as final removal of the colloidal crystal and imprinting template. The resulted 3DMIMs consisted of a three-dimensional, highly ordered and interconnected macroporous arrays with nanoscale thickness of polymer wall, in which numerous imprinted cavities were obtained. The kinetic and isothermal adsorption behavior of the 3DMIMs were investigated in detail. The results showed the 3DMIMs had a rapider mass transfer process, higher adsorption capacities and recognition specificity toward quinine compared with the traditional bulk imprinted polymers. In addition, the 3DMIMs exhibited obvious high permeability and low backpressure at high flow rate as column packing. Extraction experiments showed that the 3DMIMs could effectively separate quinine and its diastereoisomer, quinidine, directly from crude cinchona bark extract with a satisfactory selectivity and elution recovery.

Macroporous Superhydrophobic Coatings with Switchable Wettability Enabled by Smart Shape Memory Polymers

AbstractHere, a facile bottom‐up nanofabrication technology for making smart superhydrophobic coatings with switchable wettability and tunable optical properties by integrating shape memory polymers (SMPs) with templated macroporous photonic crystals is reported. Thermoresponsive shape memory efforts exhibited by a polyurethane‐based shape memory copolymer enable reversible microstructural transitions between a “memorized” permanent configuration composing of highly ordered arrays of macropores and a temporary deformed structure with collapsed macropores. The unique macroporous SMP photonic crystal arrays with large surface roughness can entrap a large portion of air in the interconnecting macropores, resulting in superior superhydrophobic properties including high apparent water contact angle (CA > 160°) and low CA hysteresis. Importantly, the shape memory‐enabled microstructural transitions lead to drastic wettability switching from superhydrophobic (CA > 160°) to hydrophobic (CA ≈ 110°) or from oleophobic (CA ≈139° for hexadecane) to oleophilic (CA ≈ 80°). The large CA tunability (>50°) coupled with the simultaneous color change from shining iridescence to colorless associated with the same microstructural transition can not only provide a noninvasive means for visually indicating the surface wetting states, this favorable coupling between the wetting and optical behaviors of macroporous SMP photonic crystal membranes can also pave the way for developing new tunable nanooptical devices.

Three-dimensional electrode design with conductive fibers and ordered macropores for enhanced capacitive deionization performance

Capacitive deionization (CDI) is a promising energy-efficient electrochemical water treatment technology and a scalable electrode having high mass loading is an essential imperative to the success of this technology. A thick CDI electrode was constructed by loading activated carbon particles as the electroactive material into a three-dimensional framework fabricated from a mixture felt of conductive carbon fiber serving as an electron transfer channel and removable yak hair functioning to provide an ion transport pathway. The carbon fiber reduces the electrode electrical resistance and the ultimately removed yak hair creates an ordered macropore array that provides an ion reservoir as well as a conduction channel for reducing ion transport distance inside the electrode. The resulting composite electrode with an optimal carbon fiber and yak hair content shows a specific capacitance of 219.27 F g−1 at 0.1 A g−1 and reaches salt adsorption capacity of 15.75 mg g−1 and average salt adsorption rate of 17.10 mg g−1 h−1 with more than 50% retention after 200 cycles. The designed three-dimensional composite exhibits enhanced deionization and long-term stability that is believed to be a low-cost and simple assembly solution for achieving a high mass loading and scalable electrode for the industrial CDI applications.

Uniform Li Plating/Stripping within Ni Macropore Arrays Enabled by Regulated Electric Field Distribution for Ultra-Stable Li-Metal Anodes.

SummaryAlthough Li-metal anodes are extremely attractive owing to the ultrahigh theoretical specific capacity, the low Coulombic efficiency and severe safety hazards resulting from uncontrollable Li dendrites growth hinder their widespread implementation. Herein, we propose a novel design of Ni macropore arrays for the functional Li deposition host. Benefiting from the regulated electric field distribution, Li nucleation and growth can be well confined within conductive Ni macropores. Consequently, the Ni macropore array electrode exhibits stable Li deposition behavior, i.e., high Coulombic efficiency of above 97% over 400 cycles for 1.0 mAh cm−2. Most importantly, the LiFePO4 || Li-Ni macropore arrays full cell also shows greatly enhanced cycling stability (90.3 mAh g−1 at 1 C after 700 cycles), holding great promise for high-performance rechargeable Li metal batteries.

ZnO@ZIF-8 inverse opal structure photoanode for efficient CdS/CdSe co-sensitized quantum dot solar cells

Photoanodes in quantum-dot-sensitized solar cells are essential to the process of light collection and charge transfer. In this paper, three-dimensional inverse opal (ZnO@ZIF-8 3D IO) photoanode is fabricated via a self-assembled opal template method. The synthesized photoanode has completely connected pores with extended diameter, thus promoting the permeability of QDs and electrolyte. Meanwhile, the light trapping ability and charge transfer process can be enhanced due to the slow photon and multi-scattering effect of the regularly interconnected macroporous array structure. ZIF-8 shell coated on the surface of ZnO IO not only provides high porosity but also serves as a protective passivation layer to reduce the carriers recombination occurred at the interfacial. In order to investigate the charge transport mechanism of ZnO @ ZIF-8 IO, cascaded CdS/CdSe quantum dots were used as sensitizers. Benefiting from the IO structure and ZIF-8 modification, the photoelectric conversion efficiency of solar cells based on ZnO@ZIF-8 IO can reach 1.75% (1.71 ± 0.04%), almost twice of that of the solar cells based on ZnO IO photoanode (0.81 ± 0.05%).

Fabrication and Electrocatalytic Performance of a Two Dimensional ß-PbO2 Macroporous Array for Methyl Orange Degradation

Fabrication and Electrocatalytic Performance of a Two Dimensional ß-PbO2 Macroporous Array for Methyl Orange Degradation

Rational construction of macroporous CoFeP triangular plate arrays from bimetal–organic frameworks as high-performance overall water-splitting catalysts

Macroporous CoFeP triangular plate arrays constructed from MOFs as high-performance overall water-splitting catalysts.