Engineering the Sulfide Semiconductor/Photoinactive-MOF Heterostructure with a Hollow Cuboctahedral Structure to Enhance Photocatalytic CO2-Epoxide-Cycloaddition Efficiency.

Providing efficient electronic transport channels has always been a promising strategy to mitigate the recombination of photogenerated charge carriers. In this study, a heterostructure composed of a semiconductor/photoinactive-metal-organic framework (MOF) was constructed to provide innovative channels for electronic transport. Prepared using a previously reported method ( Angew. Chem., Int. Ed. 2016, 55, 15301-15305) with slight modifications to temperature and reaction time, the CuS@HKUST-1 hollow cuboctahedron was synthesized. The CuS@HKUST-1 heterostructure possessed a well-defined cuboctahedral morphology with a uniform size of about 500 nm and a hollow structure with a thickness of around 50 nm. The CuS nanoparticles were uniformly distributed on the HKUST-1 shell. Structural characterization in cooperation with density functional theory (DFT) calculations revealed that CuS can effectively transfer photogenerated electrons to HKUST-1. CuS@HKUST-1 hollow cuboctahedrons were first introduced to the photocatalytic cycloaddition reaction of CO2 with epoxides, demonstrating excellent photocatalytic activity and stability at mild conditions (room temperature, solvent-free, and 1 atm CO2 pressure). The high photocatalytic performance of the CuS@HKUST-1 hollow cuboctahedron could be attributed to (1) the unique hollow cuboctahedron morphology, which provided a large specific surface area (693.1 m2/g) and facilitated the diffusion and transfer of reactants and products; and (2) CuS@HKUST-1 providing electronic transport channels from CuS to HKUST-1, which could enhance the adsorption and activation of CO2. Cu2+ carrying surplus electrons can activate CO2 to CO2-. The charge separation and transfer in the photocatalytic process can also be effectively promoted. This work provides a cost-effective and environmentally friendly approach for CO2 utilization reactions under ambient conditions, addressing the critical issue of rising atmospheric CO2 levels.

Hollow anatase TiO2 tetrakaidecahedral crystals with an active {001}/{110} redox interface toward high-performance photocatalytic activity.

The existence of the oxidation/reduction interface can promote the performance of a photocatalyst, due to its effect on the separation of photogenerated carriers and the surface reactivity. However, it is difficult to construct two sets of oxidation/reduction interfaces in a single crystal and compare their separation efficiency for photogenerated carriers. Introducing a high proportion of active facets into the co-exposed facets is even more challenging. Herein, a hollow anatase TiO2 tetrakaidecahedron (HTT) with two sets of oxidation/reduction interfaces ({001}/{101} and {001}/{110}) is synthesized by directional chemical etching. Theoretical and experimental results indicate that the {001}/{110} interface is a dominant oxidation/reduction interface, showing a better promotion on the separation of photogenerated carriers than the {001}/{101} interface. In the HTT, the ratio of dominant {001}/(110) is increased and the proportion of the active {110} facet is about 40% (generally about 15%). Therefore, the HTT shows excellent catalytic activity for photocatalytic reductive (hydrogen production) and oxidative (selective oxidation of sulfides) reactions. The HTT also demonstrates favorable photocatalytic activity for the cross-dehydrogenative coupling reaction, where both photogenerated electrons and photogenerated holes are involved, further verifying its high separation efficiency of photogenerated carriers and surface reactivity. This work provides an important guideline for developing advanced structures with a predetermined interface toward desired applications.

Enrichment Strategies for Efficient CO2 Electroreduction in Acidic Electrolytes.

Electrochemical CO2 reduction reaction (CO2 RR) has been recognized as an appealing route to remarkably accelerate the carbon-neutral cycle and reduce carbon emissions. Notwithstanding great catalytic activity that has been acquired in neutral and alkaline conditions, the carbonates generated from the inevitable reaction of the input CO2 with the hydroxide severely lower carbon utilization and energy efficiency. By contrast, CO2 RR in an acidic condition can effectively circumvent the carbonate issues; however, the activity and selectivity of CO2 RR in acidic electrolytes will be decreased significantly due to the competing hydrogen evolution reaction (HER). Enriching the CO2 and the key intermediates around the catalyst surface can promote the reaction rate and enhance the product selectivity, providing a promising way to boost the performance of CO2 RR. In this review, the catalytic mechanism and key technique challenges of CO2 RR are first introduced. Then, the critical progress of enrichment strategies for promoting the CO2 RR in the acidic electrolyte is summarized with three aspects: catalyst design, electrolyte regulation, and electrolyzer optimization. Finally, some insights and perspectives for further development of enrichment strategies in acidic CO2 RR are expounded.

Engineering cuboctahedral N-doped C-coated p-CuO/n-TiO2 heterojunctions toward high-performance photocatalytic cross-dehydrogenative coupling.

The low separation efficiency of photogenerated electron-hole (e-h) pairs severely limits the activation of photocatalyts. One brilliant strategy is to construct a p-n type semiconductor heterojunction, which can establish an inner electric field to separate the e-h pairs with high efficiency. Here, for the first time, a cuboctahedral N-doped carbon-coated CuO/TiO2 p-n heterojunction (CuO-TiO2@N-C) was designed and fabricated successfully via direct calcination of a benzimidazole-modulated cuboctahedral HKUST-Cu with titanium-tetraisopropanolate absorbed inside concomitantly. Full structural characterizations incorporating DFT computations demonstrate that the CuO/TiO2 p-n heterostructure can greatly boost the transport and separation of photoinduced e-h pairs. The nitrogen-doped carbon coating, with its excellent conductivity, porosity, stability and surface reaction activity, plays a pivotal role in promoting the overall performance and effectiveness of the reaction. The CuO-TiO2@N-C displays significantly higher photocurrent density (0.042 µA cm-2) than the CuO@N-C (0.014 µA cm-2) and TiO2@N-C (0.03 µA cm-2) electrodes, proving that the p-n heterojunction can improve the e-h generation efficiency. This unique photocatalyst affords superior photocatalytic efficiency, cycle stability and substrate scope towards cross-dehydrogenative coupling reactions.

Construction of a micro-nano reactor assembled by TiO2/N-C ultrathin sheets for photocatalytic H2 evolution.

In this paper, a series of micro-nano reactors assembled by N doped carbon coated TiO2 heterojunction nanosheets with different thickness, named TiO2/N-C hollow framework (HF), TiO2/N-C hollow hexahedron assembled by nanosheets (HHS), and TiO2/N-C hollow hexahedron assembled by ultrathin nanosheets (HHUS), have been prepared by adjusting the alcoholysis rate of NH2-MIL-125 and then pyrolysis. Experimental and theoretical studies revealed that with the decrease of the thickness of the heterojunction nanosheet subunit, more low-coordination Ti atoms would be exposed as effective sites for photocatalytic H2 evolution, and the interaction between the carbon layer and TiO2 would also be enhanced, which provided a smooth migration path for the effective separation of photogenerated carriers. Thus, TiO2/N-C HHUS with the thinnest nanosheet subunit exhibited the best photoelectric performance and the highest photocatalytic hydrogen production activity.

Electrocatalytic Overall Water Splitting Induced by Surface Reconstruction of an Iron-Modified Ni2P/Ni5P4 Heterojunction Array Encapsulated into a N-Doped Carbon Layer.

Reasonable development of high-efficiency and robust electrocatalysts for efficient electrocatalytic water splitting at high current density is hopeful for renewable energy, but the real challenge is substituting the precious metal catalysts. Herein, ultrathin Fe-modified Ni2P/Ni5P4 nanosheet arrays hybridized with N-doped carbon grown on Ni foam (Fe-Ni2P/Ni5P4@N-C) were synthesized via a solvothermal-pyrolysis strategy. Theoretical calculations and in situ Raman characterizations confirm that the Fe sites can facilitate the surface reconstruction of highly active NiOOH species and significantly lower the energy barrier for the formation of the *OOH intermediate owing to the electron coupling effect between Fe and the Ni2P/Ni5P4 heterostructure. On account of the structural advantages and compositional synergy, the optimized Fe-Ni2P/Ni5P4@N-C exhibits superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities with an overpotential of 105 and 280 mV to reach 10 and 50 mA cm-2, respectively, and can work stably for 60 h at 100 mA cm-2. Impressively, the electrolyzer with Fe-Ni2P/Ni5P4@N-C only needs 1.56 V to achieve 10 mA cm-2 current density for water splitting. This protocol not only provides inspiration for designing transitional metal electrocatalysts for water splitting but also puts forward a pathway for practical application.

N-Doped Carbon Confined NiCo Alloy Hollow Spheres as an Efficient and Durable Oxygen Electrocatalyst for Zinc-Air Batteries.

Exploring cost-efficient/durability bifunctional electrocatalysts are of upmost importance for the practical application of metal-air batteries. However, preparing bifunctional electrocatalysts with the above three advantages remains conceptually challenging. This work reports the preparation of N-doped carbon confined NiCo alloy hollow spheres (NiCo@N-C HS) as bifunctional oxygen electrocatalyst for Zn-air battery with a higher energy density (788.7 mWh gZn -1 ) and outstanding cycling stability (over 200 h), which are more durable than the commercialized Pt/C+RuO2 -based device. Electrochemical results and theoretical calculation demonstrate that the synergy in the NiCo@N-C accelerates the electronic transmission for improving activation of O2 * and OH* intermediates and optimizing reacted free energy pathways, while the hollow structures exposure more active sites for improving the reaction kinetics and enhancing the activity of ORR/OER reaction. This work provides crucial understanding for constructing low-cost transition metal-based catalyst to overcome the efficiency and durability barriers of metal-air batteries for widespread applications.

Self-supported Ni2P/NiMoP2 bimetallic phosphide with strong electronic interaction for efficient overall water splitting.

Electronic regulation via interface engineering is recognized as an attractive strategy for boosting electrocatalytic activity. In this work, a self-supported heterostructure electrocatalyst is explored by a feasible hydrothermal-pyrolysis strategy, in which Ni2P nanoparticles are anchored on NiMoP2 nanosheet arrays grown on carbon cloth (Ni2P/NiMoP2/CC). Benefitting from the nanosheet array architecture and the synergy effect between the Ni2P and NiMoP2, the as-prepared Ni2P/NiMoP2/CC manifests highly efficient activity and stability toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory calculations further indicates that the heterointerface in Ni2P/NiMoP2/CC enable optimized interface electron structure and reduce the activation barriers for intermediates, improving the intrinsic electrocatalytic activity. Remarkably, the Ni2P/NiMoP2/CC||Ni2P/NiMoP2/CC electrolyzer affords 10 mA cm-2 at a low voltage of 1.59 V, outperforming its monometallic phosphides counterparts and most of transition metal-based bifunctional electrocatalysts. The electrolyser was powered by a solar cell to produce H2 and O2 simultaneously, indicating its potential application in solar-to-hydrogen conversion.

Wedged DNA Walker Coupled with a Bimetallic Metal-Organic Framework Electrocatalyst for Rapid and Sensitive Monitoring of DNA Methylation.

The dissociation of the walking strand from the track gives rise to decreased efficiency and long reaction time of DNA walkers. In this work, we constructed a DNA walker combining the introduction of a wedge segment with a bimetallic metal-organic framework (MOF) electrocatalyst to solve this problem. The target methylated DNA acted as a single-legged walker, and the immobilization probe assembled on the track contained a wedge segment that was complementary to the target methylated DNA persistently, inhibiting its dissociation from the track. The fuel strand modified with a bimetallic MOF would drive the target strand to conduct branch migration and move processively along the track. The stepwise movement of the target strand resulted in the loading of numerous bimetallic MOF catalysts to reduce H2O2 at the electrode interface, thereby a significantly increased current response would be obtained for the detection of methylated DNA. This DNA walker achieved a detection limit of 200 aM within 20 min and effectively distinguished DNA with different methylation statuses, which would pave a way for rapid and sensitive monitoring of DNA methylation.

Immobilization of AgCl/Pd Heterojunctions on Nitrogen-Doped Carbon Nanotubes: Interfacial Design-Induced Electronic Regulation Enhances Photocatalytic Activity.

Rationally designing interface structure to modulate the electronic structure of a photocatalyst is an efficient strategy to facilitate the separation and migration of photogenerated charge carriers and improve photocatalytic activity. In this work, a AgCl/Pd heterostructure encapsulated by N-doped carbon nanotubes (AgCl/Pd@N-C) with a fan-like morphology assembled hollow tubes was synthesized by pyrolysis of a AgCl/Pd@Bim precursor. The unique interface structure not only increases the number of photogenerated charge carriers, but also provides an effective channel for the separation of electrons and holes, which have been proved by density functional theory (DFT) calculations. As expected, the obtained AgCl/Pd-3@N-C exhibited greatly enhanced conversion efficiency and recyclability toward the photocatalytic oxidative coupling of amine under blue-light irradiation.

Combination of DNA walker and Pb2+-specific DNAzyme-based signal amplification with a signal-off electrochemical DNA sensor for Staphylococcus aureus detection.

the accurate, reliable and specific analysis of foodborne pathogenic bacteria is vital for human health and safety. Staphylococcus aureus (S. aureus), as a common bacterium, is regularly found in food, water, and other biological samples. Herein, a signal-off electrochemical DNA sensor (E-DNA sensor) was designed for the sensitive detection ofS. aureusamplified withthecombination of a dna walker and pb2+-specific dnazyme. In this work, vancomycin functionalized gold nanoclusters (Van@Au NCs) and an aptamer strand as identification units were modified at the termini of two proximity probes. upon the addition of targetS. aureus, a dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pba dual-recognition binding-induced dna walker was driven by the formation of pb2+-dependent dnazyme, achieving the conversion of oneS. aureus to many intermediate dna (t) strands. then, the released t strands hybridized with methylene blue-tagged hairpin dna (h-mb) on the electrode. consequently, the conformational alteration of t strands reduced the electron transfer efficiency of mb to the electrodeinterface (signal-off). therefore, sensitive analysis of S. aureus was readily acquired within a range of 10-107 CFU/mL and a low detection limit at 1 CFU/mL. Undoubtedly, dual recognition by aptamer and vancomycin in an integrated scheme brought about a good recognition performance of S. aureus in complex samples, as well as an efficient annihilation of harmful pathogenic bacteria during the experiment.

Collaboratively boosting charge transfer and CO2 chemisorption of SnO2 to selectively reduce CO2 to HCOOH.

In this study, we have facilely developed a SnO2-based electrocatalyst (SnO2-VO@N-C), which can combine together the favorable structure features of oxygen vacancies, porosity, and full-coating with N-doped carbon layers (N-C). Our experimental and theoretical calculation results indicated that with the facile engineering of oxygen vacancies and the full-coating of the N-doped carbon layer, the adsorption/activation of CO2 and charge transfer can be promoted in the CO2 reduction process, making SnO2-VO@N-C the electrocatalyst with improved activity and selectivity (FEHCOOH = 84%) toward the reduction of CO2 to HCOOH.

Hierarchical CeO2@N-C Ultrathin Nanosheets for Efficient Selective Oxidation of Benzylic Alcohols in Water.

A monodisperse CeO2@N-C ultrathin nanosheet self-assembled hierarchical structure (USHR) has been prepared by metal-organic framework template methods. The uniform coating of nitrogen-doped carbon (N-C) layers could play an important role in the adsorption and activation of benzylic alcohol. The unique 3D hierarchical structure self-assembled by ultrathin nanosheets provided enough active sites for the catalytic reaction. Therefore, the CeO2@N-C USHR can afford excellent catalytic performance for selective oxidation of benzylic alcohols in water.

Regulating the Electronic Structure and Active Sites in Ni Nanoparticles by Coating N-Doped C Layer and Porous Structure for an Efficient Overall Water Splitting.

Developing efficient and robust bifunctional electrocatalysts are in high demand for the production of hydrogen by water splitting. Engineering an electrocatalyst with a regulated electronic structure and abundant active sites is an effective way to enhance the electrocatalytic activity. Herein, N-doped C-encapsulated Ni nanoparticles (Ni@N-C) are synthesized through a traditional hydrothermal reaction, followed by pyrolyzing under an Ar/H2 atmosphere. The electrochemical measurements and density functional theory (DFT) calculations reveal that the electron transfer between the Ni core and the N-C shell induces the electron density redistribution on Ni@N-C, which directly promotes the adsorption and desorption of H* on the N-doped carbon (N-C) layer and thus dramatically enhances hydrogen production. Taking advantage of the porous spherical structure and the synergistic effects between Ni and N-doped carbon (N-C) layer, we obtain a Ni@N-C electrocatalyst that exhibits remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity with low overpotentials of 117 and 325 mV, respectively. Impressively, the assembled cell using Ni@N-C as both anode and cathode exhibits excellent activity as well as stable cyclability for over 12 h.

Double Insurance of Continuous Band Structure and N-C Layer Induced Prolonging of Carrier Lifetime to Enhance the Long-Wavelength Visible-Light Catalytic Activity of N-Doped In2O3.

Nonmetallic doped metal oxides can be broad in their visible-light-response range. However, the half-filled or isolated impurity state can also be the new recombination center for photogenerated electrons/holes, which seriously influence the photocatalytic activity of the catalyst in the visible-light region. Therefore, how to prolong the photogenerated carrier life of nonmetallic doping metal oxides is the difficult and challenging topic in the field of photocatalysis. In this work, the hexagonal nanosheets assembled by N-doped C (N-C)-coated N-doped In2O3 (N-In2O3) nanoparticles (N-C/N-In2O3 HS) was obtained by simply pyrolyzing the In(2,5-PDC) hexagonal sheets. The N-C/N-In2O3 HS catalyst exhibit good photocatalytic activity and cycle stability in the long-wavelength region of visible light (λ = 520 and 595 nm). The effective utilization of long-wavelength visible light for N-C/N-In2O3 HS was mainly attributed to the acceptor-donor-acceptor compensation mechanism between the oxygen vacancy (VO) and substitutional N-doping (Ns) sites, which made the N-C/N-In2O3 HS possess a continuous band structure, without the half-filled or isolated impurity state in the band gap, and extended its light absorption edge to 733 nm. The compensation mechanism of nitrogen doping on In2O3 can promote the photocatalytic activity under longer-wavelength yellow light (595 nm) irradiation. The N-C layer coated on the N-In2O3 nanoparticles acted as a good acceptor of photogenerated electrons, facilitating the effective spatial separation of photogenerated carriers and extend photogenerated carrier lifetimes. The comparative photocatalytic experiments (N-In2O3 HS and N-C/N-In2O3 HS) show that the presence of N-doped C layer can enhance the photocatalytic efficiency by nearly 10-fold. This double-doping and carbon-coating strategy provided a novel research idea to solve the problem that nonmetal atoms doped metal oxides led to the secondary combination of photogenerated electrons/holes.

Hollow Dodecahedral Structure of In2O3-In2S3 Heterojunction Encapsulated by N-Doped C as an Excellent Visible-Light-Active Photocatalyst for Organic Transformation.

The low utilization efficiency in the visible region of the sunlight spectrum and the rapid recombination of photogenerated charge carriers are two crucial drawbacks that suppress the practical usage of metal oxide semiconductors as photocatalysts. In this article, we report a rational design of In2O3-In2S3 heterojunctions encapsulated by N-doped carbon with a hollow dodecahedral structure (In2O3-In2S3/N-C HDS), which can effectively handle the two drawbacks of metal oxide semiconductors and behave active for organic transformation under the irradiation of visible light even with long wavelengths. As exemplified by the selective oxidative coupling reaction of amine to imine, the obtained In2O3-In2S3/N-C HDS as the photocatalyst has exhibited excellent activity and stability. Experimental and density functional theory studies have verified that the excellent performance of In2O3-In2S3/N-C HDS can be attributed to the synergistic effect of In2O3-In2S3 heterojunctions, the coating of N-doped carbon, and the hollow porous structure with nanosheets as subunits.

Engineering Cu/TiO2@N-Doped C Interfaces Derived from an Atom-Precise Heterometallic CuII4TiIV5 Cluster for Efficient Photocatalytic Hydrogen Evolution.

Engineering interfaces is an effective method to create efficient photocatalysts by reducing the recombination of photogenerated carriers. Still, there is a lack of proficient strategies to construct suitable interfaces. In this work, we design and synthesize an atom-precise heterometallic CuII4TiIV5 cluster, [Ti5Cu4O6(ba)16]·2CH3CN (1, Hba = benzoic acid), which is used as a precursor for fabricating efficient photocatalytic interfaces. The cluster has a precise composition and structure with hierarchical bimetal atom distribution and favorable binding properties. The resulting Cu/TiO2@N-doped C interfaces are obtained via the thermal treatment. Combined Cu/TiO2 with N-doped C interfaces provide multiple channels for the transmission of photogenerated carriers and effectively reduce the recombination probability of photogenerated charge carriers. Consequently, the novel interface structure exhibits an excellent hydrogen evolution rate via the photocatalytic water splliting. Density functional theory calculations also support high activity of the interfaces toward hydrogen evolution. As a proof-of-concept application, we show that choosing well-defined metal clusters as precursors can offer a valuable method for engineering photocatalytically efficient interfaces.

Synergistic Modulation of Active Sites and Charge Transport: N/S Co-doped C Encapsulated NiCo2O4/NiO Hollow Microrods for Boosting Oxygen Evolution Catalysis.

Developing high-efficiency and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is crucial for various energy conversion systems. Herein, N/S co-doped C encapsulated hollow NiCo2O4/NiO hexagonal rods (HNHR@N/S-C) as the electrocatalysts for OER have been successfully prepared with rational control of structure and composition. Experimental and theoretical results have highlighted that the NiCo2O4/NiO heterojunction in the obtained electrocatalyst can provide abundant active Ni and Co sites for the OER, leading to the highly enhanced OER performance. Moreover, attributed to the hierarchical hollow structure, which can provide a large surface area, and the improved electric conductivity with a coating of the N/S co-doped carbon layer, which can facilitate charge transport during the catalytic processes, a remarkable OER activity over HNHR@N/S-C with a low overpotential (η) of 285 mV (at j = 10 mA cm-2) and a Tafel slope of 53.0 mV decade-1 has been achieved, which is comparable to that of the noble metal catalyst IrO2. Because of the protection of the N/S doped C layer coating, HNHR@N/S-C can also maintain the current density of 10 mA cm-2 for at least 12 h in alkaline media without obvious losses of activity.

Engineering Nickel/Palladium Heterojunctions for Dehydrogenation of Ammonia Borane: Improving the Catalytic Performance with 3D Mesoporous Structures and External Nitrogen-Doped Carbon Layers.

Catalysts based on metallic NPs have shown high activities in heterogeneous catalysis, due to their high fractions of surface-active atoms, which, however, will lead to the sacrifices in stability and recycle of catalysts. In order to balance well the relationship between activity, stability, and recovery, in this paper, we have constructed a 3D mesoporous sphere structure assembled by N-doped carbon coated Ni/Pd NP heterojunctions (Ni/Pd@N-C). This obtained Ni/Pd@N-C has shown high catalytic activity, durability and recyclability for the hydrolytic dehydrogenation of ammonia borane (AB). Further investigations, including experimental and theoretical results, have shown that the unique structural features, the synergistic effect between Ni and Pd, and the coating of N-doped carbon layer are responsible for the good catalytic performance of Ni/Pd@N-C mesoporous spheres.

Construction of an Electrochemical Biosensing Platform Based on Hierarchical Mesoporous NiO@N-Doped C Microspheres Coupled with Catalytic Hairpin Assembly.

A critical challenge for improving the detection performance of sensors is building a favorable sensing interface. Herein, an innovative electrochemical biosensing system relying on hierarchical mesoporous NiO@N-doped C microspheres coupled with catalytic hairpin assembly was developed for DNA analysis. In this strategy, the utilization of NiO@N-doped C microspheres and multiwalled carbon nanotubes as electrode materials effectively enhanced the interfacial electron transfer and improved the surface active sites for subsequent reactions. By designing a target-assisted catalytic hairpin assembly, single target DNA could initiate the introduction of multiple signal probes labeled with ferrocene (Fc) onto a working electrode surface. Because the change in the Fc signal is dependent on the amount of target DNA, the resulting electrochemical sensing platform is highly sensitive. Under optimized reaction conditions, this testing platform has a wide linear range for target DNA detection from 100 aM to 100 pM with a detection limit of 45 aM. Furthermore, the platform displayed excellent selectivity, acceptable reproducibility, and long-term stability, highlighting the application potential of this sensing system.