A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Photocatalysis is a green technology to use ubiquitous and intermittent sunlight. The emerging S-scheme heterojunction has demonstrated its superiority in photocatalysis. This article covers the state-of-the-art progress and provides new insights into its general designing criteria. It starts with the challenges confronted by single photocatalyst from the perspective of energy dissipation by borrowing the common behaviors in the dye molecule. Subsequently, other problems faced by single photocatalyst are summarized. Then a viable solution for these problems is the construction of heterojunctions. To overcome the problems and mistakes of type-II and Z-scheme heterojunctions, S-scheme heterojunction is proposed and the underlying reaction mechanism is summarized. Afterward, the design principles for S-scheme heterojunction are proposed and four types of S-scheme heterojunctions are suggested. Following this, direct characterization techniques for testifying the charge transfer in S-scheme heterojunction are presented. Finally, different photocatalytic applications of S-scheme heterojunctions are summarized. Specifically, this work endeavors to clarify the critical understanding on curved Fermi level in S-scheme heterojunction interface, which can help strengthen and advance the fundamental theories of photocatalysis. Moreover, the current challenges and prospects of the S-scheme heterojunction photocatalyst are critically discussed. 

Emerging S‐Scheme Photocatalyst

Facile fabrication of TaON/Bi2MoO6 core–shell S-scheme heterojunction nanofibers for boosting visible-light catalytic levofloxacin degradation and Cr(VI) reduction

Reasonable design of efficient hierarchical photocatalysts has gained significant attention. Herein, a step-scheme (S-scheme) core-shell TiO2 @ZnIn2 S4 heterojunction is designed for photocatalytic CO2 reduction. The optimized sample exhibits much higher CO2 photoreduction conversion rates (the sum yield of CO, CH3 OH, and CH4 ) than the blank control, i.e., ZnIn2 S4 and TiO2 . The improved photocatalytic performance can be attributed to the inhibited recombination of photogenerated charge carriers induced by S-scheme heterojunction. The improvement is also attributed to the large specific surface areas and abundant active sites. Meanwhile, S-scheme photogenerated charge transfer mechanism is testified by in situ irradiated X-ray photoelectron spectroscopy, work function calculation, and electron paramagnetic resonance measurements. This work provides an effective strategy for designing highly efficient heterojunction photocatalysts for conversion of solar fuels.

In situ Irradiated XPS Investigation on S-Scheme TiO2@ZnIn2S4 Photocatalyst for Efficient Photocatalytic CO2 Reduction

S-Scheme photocatalyst TaON/Bi2WO6 nanofibers with oxygen vacancies for efficient abatement of antibiotics and Cr(VI): Intermediate eco-toxicity analysis and mechanistic insights

Photocatalytic CO2 conversion into solar fuels has been a promising strategy to utilize abundant solar energy and alleviate greenhouse effect. Herein, a series of polydopamine-modified TiO2 (TiO2@PDA) hollow spheres were fabricated by in situ self-polymerization of dopamine to systematically investigate the effect of PDA wrapping on the photocatalytic CO2 reduction activities of TiO2. Among all TiO2@PDA composite photocatalysts, the highest value of methane yield (1.50 μmol h−1 g−1) was achieved with 0.5 % PDA, which was 5 times than that of pure TiO2 (0.30 μmol h−1 g−1). The improvement of photocatalytic activity and methane selectivity was ascribed to the enhanced light absorption, promoted CO2 adsorption capacity, increased reduction power of photogenerated electrons, as well as efficient separation and transfer of photogenerated charge carriers induced by the S-scheme heterojunction between TiO2 and PDA. This work provides a facile surface modification method with cost-effective polymer materials in photocatalytic CO2 conversion.

TiO2/polydopamine S-scheme heterojunction photocatalyst with enhanced CO2-reduction selectivity

Broadening the absorption of light to the near-infrared (NIR) region is important in photocatalysis to achieve efficient solar-to-fuel conversion. NIR-responsive photocatalysts that can utilize diffusive solar energy are attractive for alleviating the energy crisis and environmental pollution. Over the past few years, considerable progress on the component and structural design of NIR-responsive photocatalysts have been reported. This study aims to systematically summarize recent progress toward the material design and mechanism optimization of NIR-responsive photocatalysts in this area. Depending on the main strategies for harvesting NIR photons, NIR-responsive photocatalysts can be categorized as direct NIR-light photocatalysts, indirect NIR-light photocatalysts, and photothermal photocatalysts. Furthermore, the construction and application of different NIR-responsive photocatalytic systems are summarized. Conclusions and perspectives are presented to further explore the potential of NIR-responsive photocatalysts in this field.

Near-Infrared-Responsive Photocatalysts

Tuning the strength of built-in electric field in 2D/2D g-C3N4/SnS2 and g-C3N4/ZrS2 S-scheme heterojunctions by nonmetal doping

Solar-driven semiconductor photocatalysis shows great potential to solve growing energy and environmental crises. Electrospun TiO2 nanofibers (NFs) attract attention due to their chemical stability, nontoxicity, cheapness, large specific surface area, and porous structures. The unique unwoven nanofibrous network facilitates mass transportation compared with bulk materials. Electrospun TiO2 NFs are an ideal substrate for growing secondary nanostructures and constructing heterojunction photocatalysts. The hybrid heterojunctions show enhanced electron–hole separation, improved light absorption, effective activation of reactants, and therefore increased photocatalytic performance. Herein, the electrospinning principle and preparing tactics of electrospun TiO2 fibrous nanostructures including solid, hollow, and core/shell NFs are first described. The construction strategies of electrospun TiO2-based heterojunctions by loading electron or hole cocatalysts and hybridizing secondary semiconductors to engineer catalytic active sites and steer charge carrier separation are outlined. Dopant-induced increased light absorption and enhanced charge transfer of TiO2 NFs are discussed. Further, the applications of electrospun TiO2-based photocatalysts for solar-to-chemical conversion and environmental remediation are elucidated. Finally, the challenges and perspectives for the development of electrospun TiO2-based photocatalysts are underlined, which deepen a systematic understanding of the design and fabrication of more efficient electrospun NFs in the future.

Haiyan Tan

Papers

TiO2/polydopamine S-scheme heterojunction photocatalyst with enhanced CO2-reduction selectivity

Near-Infrared-Responsive Photocatalysts

Tuning the strength of built-in electric field in 2D/2D g-C3N4/SnS2 and g-C3N4/ZrS2 S-scheme heterojunctions by nonmetal doping

Electrospun TiO2-Based Photocatalysts