Crossover behavior in stress relaxations of poroelastic and viscoelastic dominant hydrogels.

The mechanical response and relaxation behavior of hydrogels are crucial to their diverse functions and applications. However, understanding how stress relaxation depends on the material properties of hydrogels and accurately modeling relaxation behavior at multiple time scales remains a challenge for soft matter mechanics and soft material design. While a crossover phenomenon in stress relaxation has been observed in hydrogels, living cells, and tissues, little is known about how the crossover behavior and characteristic crossover time depend on material properties. In this study, we conducted systematic atomic-force-microscopy (AFM) measurements of stress relaxation in agarose hydrogels with varying types, indentation depths, and concentrations. Our findings show that the stress relaxation of these hydrogels features a crossover from short-time poroelastic relaxation to long-time power-law viscoelastic relaxation at the micron scale. The crossover time for a poroelastic-dominant hydrogel is determined by the length scale of the contact and diffusion coefficient of the solvent inside the gel network. In contrast, for a viscoelastic-dominant hydrogel, the crossover time is closely related to the shortest relaxation time of the disordered network. We also compared the stress relaxation and crossover behavior of hydrogels with those of living cells and tissues. Our experimental results provide insights into the dependence of crossover time on poroelastic and viscoelastic properties and demonstrate that hydrogels can serve as model systems for studying a wide range of mechanical behaviors and emergent properties in biomaterials, living cells, and tissues.

Constructing Z-scheme 1D/2D heterojunction of ZnIn2S4 nanosheets decorated WO3 nanorods to enhance Cr(VI) photocatalytic reduction and rhodamine B degradation.

Photocatalysis has been vastly employed as a feasible and efficient strategy for the removal of environmental pollutants. In this study, a well-designed core-shell heterojunction of WO3 decorated with ZnIn2S4 nanosheets were fabricated under mild in-situ conditions, and fabricated processes were systematically investigated with different fabrication durations. The coupling of WO3 and ZnIn2S4 (ZIS) resulted in a Z-scheme mechanism for charge carrier transfer, holding the respective redox capacity. The as-prepared 1D/2D WO3@ZIS heterostructure displayed the highest removal efficiency within 30 min for 25 mg L-1 Cr(VI), 89.3 and 29.7 times higher than pure WO3 and ZnIn2S4. 1D/2D WO3@ZIS remained excellently stable after 5 cycling experiments. Moreover, 40 mg L-1 RhB could be degraded within 50 min. The broad and short photogenerated electron transportation path is guaranteed by the 1D/2D and Z-scheme charge separation mechanism. It efficiently prevented photo-generated charge carriers from recombination, resulting in a longer carrier lifespan and better photocurrent responses than that of pure ones. This photocatalytic system showed promising results and also provides a framework for an efficient system for photocatalysis with potential for environmental application.

Engineering BiVO4@Bi2S3 heterojunction by cosharing bismuth atoms toward boosted photocatalytic Cr(VI) reduction.

The photocatalytic efficiency is limited by poor charge separation efficiency and high carrier transport activation energy (CTAE) of photogenerated electron/hole pairs than traditional semiconductor. Hybridizing nanostructure with two staggered alignment band structure is proved as an effective strategy to mitigate these two challenges but still suffers a strong coulomb electrostatic repulsive force between two heterogeneous semiconductors. Here, we steer a friendly sulfurization process to construct BiVO4@Bi2S3 heterojunction with a scenario of cosharing Bi atoms. The intimate atomic-level contact between BiVO4 and Bi2S3 not only enhances the visible-light absorption and lowers CTAE, but also accelerate carrier's separation efficiency, which enables it to deliver the best photocatalytic performance toward reduction of Cr(VI). BiVO4@Bi2S3 only needs less than 40 min to completely reduce 50 ppm Cr(VI) solution. The type II heterojunction photocatalytic mechanism is systematically studied to decipher the carriers' transfer track between BiVO4 and Bi2S3. Our new finding of engineering inorganic heterojunction by cosharing atoms opens a new avenue to other similar materials for potential applications.

Unveiling the Synergistic Effect between Graphitic Carbon Nitride and Cu2 O toward CO2 Electroreduction to C2 H4.

Electrochemically reducing carbon dioxide (CO2 RR) to ethylene is one of the most promising strategies to reduce carbon dioxide emissions and simultaneously produce high value-added chemicals. However, the lack of catalysts with excellent activity and stability limits the large-scale application of this technology. In this work, a graphitic carbon nitride (g-C3 N4 )-supported Cu2 O composite was fabricated, which exhibited a 32.2 % faradaic efficiency of C2 H4 with a partial current density of -4.3 mA cm-2 at -1.1 V vs. reversible hydrogen electrode in 0.1 m KHCO3 electrolyte. The introduction of g-C3 N4 support not only enhanced the uniform dispersion of Cu2 O nanocubes, but also stabilized the important *CO intermediates. Moreover, the g-C3 N4 itself had a good activity of reducing CO2 to form *CO, which enriched the key intermediates of C-C coupling around cuprous oxide. The findings highlight the importance of the g-C3 N4 support, a unique two-dimensional material, including not only the strong CO2 adsorption and activation capacity but also its synergistic effect with the cuprous oxide in CO2 RR selectivity.

Enhancing the photocatalytic activity of ZnSn(OH)6 achieved by gradual sulfur doping tactics.

To solve the intrinsic deficiency inherited from the large band gap of ZnSn(OH)6 (ZSH), a gradual sulfur doping strategy is first proposed here to expand the optical absorption range, improve the separation efficiency of photogenerated electron-hole pairs, and thus enhance the photocatalytic activity. It is demonstrated that the distribution of sulfur in the flower-like ZSH (the sulfur doped sample is denoted as S-ZSH) tends to be largest on the outer most surface and becomes smaller towards the interior. The S-ZSH therefore has a gradual bandgap structure that is beneficial for transferring photogenerated charge carriers from the interior to the surface, which will greatly enhance the utilization of photoelectrons. As a result, the visible light photocurrent density of S-ZSH and the photocatalytic degradation rate of rhodamine (RhB) are about 5 and 10 times higher than with pristine ZSH, respectively.

Thermally stable core-shell Ni/nanorod-CeO2@SiO2 catalyst for partial oxidation of methane at high temperatures.

During partial oxidation of methane (POM), the greatest challenge is to maintain the thermal stability of the catalyst at high temperatures. One of the most effective ways to improve thermal stability is to construct core-shell structure. Herein, using a microemulsion method, we synthesized a core-shell Ni/nanorod-CeO2@SiO2 catalyst, in which the Ni nanoparticles were supported on the CeO2 nanorods and encapsulated by SiO2 shells. Based on a series of characterizations, we found that the Ni particles are of nanosize (2.2 nm) and the thickness of the SiO2 shell is about 8 nm in the core-shell catalyst. Moreover, the Ni/nanorod-CeO2@SiO2 catalyst can perfectly maintain rod-like structures of the CeO2 support and enhance interaction between the metal Ni and CeO2, significantly reducing the sintering of metal Ni particles at high temperatures. Therefore, the as-prepared Ni/nanorod-CeO2@SiO2 catalyst shows high catalytic activity and good thermal stability during the POM reaction.