Ternary Bi2S3/MoS2/TiO2 with double Z-scheme configuration as high performance photocatalyst

Due to unique electron transport properties, nanostructured catalysts with certain morphology, such as nanotube, nanosheet and nanorods, have shown outstanding photocatalytic performance. Herein, preparation of ternary photocatalytic architecture is demonstrated using a facile microwave-assisted hydrothermal method. The as-prepared ternary photocatalyst (denoted as Bi2S3/MoS2/TiO2) comprises bismuth sulfide (Bi2S3) nanorods, molybdenum sulfide (MoS2) nanosheets, and titanium dioxide (TiO2) nanotubes. The photocatalytic performance of the as-prepared nanocomposite is evaluated by monitoring water splitting and dye degradation. The results show that the Bi2S3/MoS2/TiO2 exhibits stable and highly efficient photocatalytic hydrogen production under visible light, and photocatalytic degradation of methylene blue (MB) under sunlight. The photocatalytic performance of Bi2S3/MoS2/TiO2 is much better than that of TiO2, MoS2, or Bi2S3. The improved performance is correlated to the high surface area and the formation of the double Z-scheme heterostructure, which together render abundant catalytic sites and efficient charge separation with strong redox capability. Additionally, X-ray photoelectron spectroscopy and electron spin resonance spectroscopies, combined with reactive species trapping experiments, confirm that the surface charge transport in Bi2S3/MoS2/TiO2 occurs through the double Z-scheme approach. This work paves the way for designing more photocatalytic systems with double Z-scheme for high efficiency and wide practical applications

Synthesis of heterostructured Bi2O3–CeO2–ZnO photocatalyst with enhanced sunlight photocatalytic activity

The development of heterostructured semiconductor photocatalysts makes a noteworthy advancement in environmental purification technology. In this work, a novel heterostructured Bi2O3−CeO2−ZnO, fabricated by a combination of microwave-assisted hydrothermal and thermal decomposition methods, showed an enhanced photocatalytic activity for Rhodamine B (RhB) degradation under sunlight, as compared to pristine ZnO, Bi2O3, CeO2, and commercial Degussa TiO2-P25. The obtained products were thoroughly characterized by various techniques including X- ray powder diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), elemental color mapping, energy-dispersive X-ray spectroscopy (EDAX), Raman spectrometry, Fourier transform infrared (FT-IR) spectroscopy, UV–visible diffuse reflectance spectroscopy (UV–vis DRS), and photoluminescence (PL) spectroscopy. PXRD analysis reveals that the heterostructure has the monoclinic lattice phase of α-Bi2O3, the cubic phase of CeO2 and the hexagonal wurtzite phase of ZnO. FE-SEM images show that Bi2O3−CeO2−ZnO has an ordered mixture of nanorod and nanochain structures. EDAX, elemental color mapping, Raman and FT-IR analyses confirm the successful formation of the heterostructured Bi2O3−CeO2−ZnO. The UV–Vis DRS results demonstrate that Bi2O3−CeO2−ZnO exhibits wide visible-light photoabsorption in 400–780nm range. Moreover, the reduction in PL intensity of the heterostructured Bi2O3−CeO2−ZnO, when compared to the pristine Bi2O3, CeO2, and ZnO, indicates enhanced charge separation. The study on the mechanism displayed that the improved photocatalytic activity of Bi2O3−CeO2−ZnO could be attributed to (1) the efficient separation of photoinduced electrons and holes of the photocatalysts, caused by the vectorial transfer of electrons and holes among ZnO, CeO2 and Bi2O3, and (2) the wide visible-light photoabsorption range. This study introduces a new class of promising sunlight-driven photocatalysts

The correlation among morphology, oxygen vacancies and properties of ZnO nanoflowers

Despite numerous reports have investigated the effect of morphology on the properties of nanomaterials, its role in tuning nanomaterials properties is still not clear to date. This work introduces a unique attempt to explore the correlation among morphology, surface defects (oxygen vacancies), and properties of nanomaterials. To achieve this task, three different morphologies of ZnO nanoflowers were prepared via hydrothermal method by varying the concentration of diethylamine. It was observed that a change in ZnO nanoflowers morphology results in changes in their optical, photocatalytic, and antibacterial properties. Photoluminescence and X-ray photoelectron spectroscopy analyses reveal the presence of oxygen vacancies (VO) in ZnO nanoflowers with a concentration varies with respect to morphology. VO concentration plays a key role in tuning ZnO band gap and the concentration of reactive oxygen species and thereby tuning optical, photocatalytic, and antibacterial properties of ZnO nanoflowers. Our results suggest that VO concentration, morphology, and properties of ZnO nanoflowers are correlated

Laser-assisted synthesis of Z-scheme TiO2/rGO/g-C3N4 nanocomposites for highly enhanced photocatalytic hydrogen evolution

Constructing nanocomposite structures with favorable charge transfer routes is an effective way to obtain highly efficient photocatalysts. Herein, fabrication of indirect and noble metal-free Z-scheme photocatalytic architecture is demonstrated using pulsed laser ablation in liquids (PLAL) technique for the first time. The as-prepared ternary photocatalyst (denoted as TiO2/rGO/g-C3N4) comprises titanium dioxide (TiO2) nanotubes, reduced graphene oxide (rGO) nanosheets, and graphitic carbon nitride (g-C3N4) nanosheets. The photocatalytic activity of the as-synthesized composite is evaluated by monitoring water splitting. Various analytical techniques were employed to investigate the compositional, morphological, structural, and optical properties of the photocatalysts. The system of TiO2/rGO/g-C3N4 with the weight ratio of TiO2 to g-C3N4 of 2:4 and 1% rGO exhibited the highest hydrogen production rate of 32 +/- 1 mmol g(-1)h(-1), which is about 93, 3.8 and 2.6 times higher than those of pure g-C3N4, TiO2, and TiO2/rGO, respectively. This enhanced performance can be ascribed to the strong interfacial bonding (TiO2/rGO/g-C3N4), extended visible light absorption capacity due to higher photo-responsiveness of rGO and g-C3N4, the synergetic effect between TiO2 and g-C3N4 and direct contact between TiO2 and rGO which facilitated efficient separation and transfer of photogenerated charges. This study opens opportunities for the fabrications of different Z-scheme systems for various applications

Direct Z-scheme Cs2O-Bi2O3-ZnO heterostructures for photocatalytic overall water splitting

In this work, a direct Z-scheme Cs2O-Bi2O3-ZnO heterostructure without any electron mediator is fabricated by a simple solution combustion route. Cs2O is chosen as a sensitizer to expand the light absorption range, and in addition, its conduction band minimum (CBM) and valence band maximum (VBM) positions are suitable to construct a direct Z-scheme system with ZnO and Bi2O3. Structural and elemental analyses show clear evidence for heterostructure formation. The Z-scheme charge carrier migration pathway in Cs2O-Bi2O3-ZnO is confirmed by high resolution XPS and ESR studies. The fabricated heterostructure exhibits a good ability to split water to H2 and O2 under simulated sunlight irradiation without any sacrificial agents or co-catalysts and has excellent photostability. The apparent quantum efficiency of the optimized Cs2O-Bi2O3-ZnO heterostructure reaches up to 0.92% at 420 nm. The excellent efficiency of this fabricated heterostructure is attributed to the efficient charge carrier separation, the high redox potential of the CBM and VBM benefiting from a direct Z-scheme charge carrier migration pathway and the extended light absorption range. © The Royal Society of Chemistry

Mechanical Performance of Date-Palm-Fiber-Reinforced Concrete Containing Silica Fume

The use of date palm fiber (DPF) as natural fiber in concrete and mortar continues to gain acceptability due to its low-cost and availability. However, the main disadvantage of DPF in cement-based composites is that it reduces compressive strength and increases the porosity of the composite. Hence, for DPF to be efficiently used in concrete, its negative effects must be counteracted. Therefore, in this study, silica fume was employed as supplementary cementitious material to alleviate the negative effects of DPF on the strength and porosity of concrete. The DPF was added in different dosages of 0%, 1%, 2%, and 3% by weight of binder materials. Silica fume was used as a cement replacement material at dosages of 0% to 15% (intervals of 5%) by volume of cement. The unit weights, mechanical strengths, water absorption, and microstructural morphology were all evaluated. The concrete’s fresh and hardened densities were reduced with the increment in DPF and silica fume. The compressive strength declined at all ages with the increment in DPF addition, while the flexural and splitting tensile strengths improved with addition of up to 2% DPF. Furthermore, the concrete’s water absorption escalated with an increase in DPF content. Silica fume significantly enhanced the mechanical strength of the concrete. The dissipation in compressive strength with the addition of up to 2% DPF was mitigated by replacing up to 10% cement with silica fume, where it densified the microstructure and refined the interfacial transition zone between the fibers and cement matrix, hence significantly decreasing the porosity and enhancing durability

Direct Z‑Scheme Cs2O–Bi2O3–ZnO Heterostructures as Efficient Sunlight-Driven Photocatalysts

Limited light absorption, inefficient electron–hole separation, and unsuitable positions of conduction band bottom and/or valence band top are three major critical issues associated with high-efficiency photocatalytic water treatment. An attempt has been carried out here to address these issues through the synthesis of direct Z-scheme Cs2O–Bi2O3–ZnO heterostructures via a facile, fast, and economic method: solution combustions synthesis. The photocatalytic performances are examined by the 4-chlorophenol degradation test under simulated sunlight irradiation. UV–vis diffuse reflectance spectroscopy analysis, electrochemical impedance test, and the observed transient photocurrent responses prove not only the significant role of Cs2O in extending light absorption to visible and near-infrared regions but also its involvement in charge carrier separation. Radical-trapping experiments verify the direct Z-scheme approach followed by the charge carriers in heterostructured Cs2O–Bi2O3–ZnO photocatalysts. The Z-scheme charge carrier pathway induced by the presence of Cs2O has emerged as the reason behind the efficient charge carrier separation and high photocatalytic activity

Mechanical Performance of Date-Palm-Fiber-Reinforced Concrete Containing Silica Fume

The use of date palm fiber (DPF) as natural fiber in concrete and mortar continues to gain acceptability due to its low-cost and availability. However, the main disadvantage of DPF in cement-based composites is that it reduces compressive strength and increases the porosity of the composite. Hence, for DPF to be efficiently used in concrete, its negative effects must be counteracted. Therefore, in this study, silica fume was employed as supplementary cementitious material to alleviate the negative effects of DPF on the strength and porosity of concrete. The DPF was added in different dosages of 0%, 1%, 2%, and 3% by weight of binder materials. Silica fume was used as a cement replacement material at dosages of 0% to 15% (intervals of 5%) by volume of cement. The unit weights, mechanical strengths, water absorption, and microstructural morphology were all evaluated. The concrete’s fresh and hardened densities were reduced with the increment in DPF and silica fume. The compressive strength declined at all ages with the increment in DPF addition, while the flexural and splitting tensile strengths improved with addition of up to 2% DPF. Furthermore, the concrete’s water absorption escalated with an increase in DPF content. Silica fume significantly enhanced the mechanical strength of the concrete. The dissipation in compressive strength with the addition of up to 2% DPF was mitigated by replacing up to 10% cement with silica fume, where it densified the microstructure and refined the interfacial transition zone between the fibers and cement matrix, hence significantly decreasing the porosity and enhancing durability

Electronically semitransparent ZnO nanorods with superior electron transport ability for DSSCs and solar photocatalysis

Oxygen vacancies (VO) as intrinsic defects play a key role in determining zinc oxide (ZnO) properties. Herein, ZnO nanorods with uniform morphology have been synthesized via hydrothermal method. The obtained nanorods appear semitransparent in SEM images indicating their electron semitransparent nature (ESN). Dye sensitized solar cells (DSSCs) studies reveal the superior electron transport property of the prepared nanorods further confirming their ESN. XPS, optical absorption, and DSSCs results suggest that the origin of ESN is the presence of an appropriate amount of VO in the ZnO nanorods. Moreover, the obtained ZnO nanorods exhibit excellent photocatalytic activity in decomposition of phenol under sunlight irradiation which is attributed to VO. Our study introduces a fundamental insight into the role of VO in inducing ESN as a new property for ZnO