Biosynthesis of zinc oxide nanoparticles using Euphorbia milii leaf constituents: Characterization and improved photocatalytic degradation of methylene blue dye under natural sunlight

A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m²/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm³/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm^?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.     

Durian waste mediated green synthesis of zinc oxide nanoparticles and evaluation of their antibacterial,antioxidant, cytotoxicity and photocatalytic activity

ABSTRACT

The synthesized ZnO NPs using durian rind in solution has shown maximum absorption at 355.5?nm with the bandgap of 3.33?eV, spectrophotometrically. SEM and TEM studies revealed that the shape of the synthesized ZnO NPs was spherical with an average size of 280 and 283?nm, respectively. However, DLS analysis of ZnO NPs revealed the average particle size of 456?d.nm. The presence of [100], [002], [101], [102], [110], [103], [200], [112] and [201] planes in XRD corroborate the formation of pure wurtzite structure of ZnO NPs. Synthesized ZnO NPs showed remarkable photocatalytic activity on degradation of methylene blue and sulfanilamide, antioxidant activity, considerable antimicrobial activity against Escherichia coli and Staphylococcus aureus, and considerable cytotoxic activity against brine shrimp. The sulfanilamide degradation was found to be 96.70%, under natural sunlight and in the presence of 0.1% ZnO NPs at pH 10 with a time of 3?h. The dye degradation was found to be 84% under sunlight in the presence of 0.01% ZnO NPs at pH 10 with a time of 40?min. The synthesized ZnO NPs may be explored furthermore in the fields of wastewater treatment, biomedicine, biosensor, and nanotechnology.     

Sunlight Photocatalytic Performance of ZnO Nanoparticles Synthesized by Green Chemistry Using Different Botanical Extracts and Zinc Acetate as a Precursor

In this work, the assessment of Azadirachta indica, Tagetes erecta, Chrysanthemum morifolium, and Lentinula edodes extracts as catalysts for the green synthesis of zinc oxide nanoparticles (ZnO NPs) was performed. The photocatalytic properties of ZnO NPs were investigated by the photodegradation of methylene blue (MB) dye under sunlight irradiation. UV-visible (UV-Vis) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Thermogravimetric (TGA), and Brunauer-Emmett-Teller analysis (BET) were used for the characterization of samples. The XRD results indicate that all synthesized nanoparticles have a hexagonal wurtzite crystalline structure, which was confirmed by TEM. Further, TEM analysis proved the formation of spherical and hemispherical nanoparticles of ZnO with a size in the range of 14–32 nm, which were found in aggregate shape; such a size was well below the size of the particles synthesized with no extract (~43 nm). ZnO NPs produced with Tagetes erecta and Lentinula edodes showed the best photocatalytic activity, matching with the maximum adsorbed MB molecules (45.41 and 58.73%, respectively). MB was completely degraded in 45 min using Tagetes erecta and 120 min using Lentinula edodes when subjected to solar irradiation.     

Heterointerface Engineering of ZnO/CdS Heterostructures through ZnS Layers for Photocatalytic Water Splitting

Solar-driven water splitting to produce clean and renewable hydrogen offers a green strategy to address the energy crisis and environmental pollution. Heterostructure catalysts are receiving increasing attention for photocatalytic hydrogen generation. ZnO/ZnS/CdS and ZnO/CdS heterostructures have been successfully designed and prepared according to two different strategies. By introducing a heterointerface layer of ZnS between ZnO and CdS, a Z scheme charge-transfer channel was promoted and achieved superior photocatalytic performance. A highest hydrogen generation rate of 156.7 μmol g⁻¹ h⁻¹ was achieved by precise control of the thickness of the heterointerface layer and of the CdS shell. These findings demonstrated that heterostructures are promising catalysts for solar-driven water splitting, and that heterointerface engineering is an effective way to improve the photocatalytic properties of heterostructures.     

The surface modification of spherical ZnO with Ag nanoparticles: A novel agent,biogenic synthesis,catalytic and antibacterial activities

Nowadays, the industrial wastewater pollutants including toxic dyes and pathogenic microbes have caused serious environmental contaminations and human health problems. In the present study, eco-friendly and facile green synthesis of Ag modified ZnO nanoparticles (ZnO-Ag NPs) using Crataegus monogyna (C. monogyna) extract (ZnO-Ag@CME NPs) is reported. The morphology and structure of the as-biosynthesized product were characterized by field emission scanning electron microscopy (FESEM), X-Ray diffraction (XRD), differential reflectance spectroscopy (DRS), dynamic light scattering (DLS), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and energy-dispersive X-ray spectroscopy (EDS) techniques. TEM and FESEM images confirmed the oval and spherical-like structure of the products with a size of 55–70 nm. The EDS analysis confirmed the presence of Zn, Ag, and O elements in the biosynthesized product. The photocatalytic results showed ZnO-Ag@CME NPs were degraded (89.8% and 75.3%) and (94.2% and 84.7%) of methyl orange (MO) and basic violet 10 (BV10), under UV and sunlight irradiations, respectively. The Ag modified ZnO nanoparticles exhibited enhanced catalytic activity towards organic pollutants, and showed better performance than the pure ZnO nanoparticles under UV and sunlight irradiations. This performance was probably due to the presence of silver nanoparticles as a plasmonic material. Antibacterial activity was performed against different bacteria. ZnO-Ag@CME NPs showed high antibacterial activity against K. pneumoniae, S. typhimurium, P. vulgaris, S. mitis, and S. faecalis with MIC values of 50, 12.5, 12.5, 12.5, and 12.45 µg/mL, respectively. All in all, the present investigation suggests a promising method to achieve high-efficiency antibacterial and catalytic performance.     

花形ZnO纳米片微球的合成、表征及光催化性能

以ZnCl2和尿素为原料,采用水热法合成了由纳米片组成的花形微球碱式碳酸锌前驱体,然后在300℃下煅烧0.5 h得到了形貌一致的ZnO产物。采用XRD、FTIR、TG、SEM、TEM、XPS对其进行表征,结果表明产物为六方纤维矿结构ZnO;组成3D花型微球的纳米片构筑单元厚度为10 nm,表面呈孔装结构,比表面积为72 m2.g-1。分别以花形ZnO纳米片、单分散ZnO纳米片和商用ZnO纳米颗粒为光催化剂,通过降解罗丹明B(Rh B)进行了光催化活性研究。结果表明,与商用ZnO纳米颗粒相比,水热法制备的花形ZnO纳米片显示了更好的光催化活性,可能是由于花形ZnO纳米片微球有较高的比表面积和3D花形形貌所致。     

微/纳米ZnO绒球的制备及其在自然光下催化降解有机染料性能

以谷氨酸氟硼酸(GluBF₄)离子液体水溶液为反应介质,以物质的量比为1:6的二水合醋酸锌[Zn(Ac)₂·2H₂O]和氢氧化钠为原料,室温下制备前驱体,再微波辅助加热制备了纳米氧化锌粉体,获得了纳米结构微米尺寸纳米ZnO绒球.利用场发射扫描电镜(FESEM)、X射线衍射(XRD)、比表面(BET)、能量色散谱(EDS)等对产物进行了表征.所得产物为六方晶系纤锌矿结构,粉体粒径20.4 nm,绒球比表面积为28.3 m²·g^-1,产物纯度较高,收率95.3%.同时探讨了纳米ZnO绒球生成的可能机理.该纳米材料在日光下显示较高的光催化活性和稳定性.分别配制浓度为10 mg·L^-1的100 mL甲基橙(MO)和甲基紫(MV)水溶液, 30 mg纳米氧化锌为光催化降解催化剂,太阳光激发下5 h脱色率分别达到74.3%和96.9%;溶液总有机碳(TOC)含量随光降解的进行缓慢下降;光催化剂重复利用5次,催化剂形貌不变、颜色不变,质量基本未发生变化.     

Azo dyes degradation using TiO2-Pt/graphene oxide and TiO2-Pt/reduced graphene oxide photocatalysts under UV and natural sunlight irradiation

The photocatalytic degradation of azo dyes with different structures (amaranth, sunset yellow and tartrazine) using TiO₂-Pt nanoparticles (TPt), TiO₂-Pt/graphene oxide (TPt-GO) and TiO₂-Pt/reduced graphene oxide (TPt-rGO) composites were investigated in the presence of UV and natural sunlight irradiation. The composites were prepared by a combined chemical-thermal method and characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRD), Infrared (FTIR) and UV–Vis spectroscopy. The modification of TiO₂-Pt with graphene oxide shifted its optical absorption edge towards the visible region and increased its photocatalytic activity under UV and natural sunlight irradiation. The efficiency of catalysts on azo dyes degradation (in similar conditions) reached high values (above 99%) under sunlight conditions, proving the remarkable photocatalytic activities of obtained composites. TPt-GO nanocomposite exhibited higher photoactivity than TPt or TPt-rGO, demonstrating degradation efficiencies of 99.56% for amaranth, 99.15% for sunset yellow and 96.23% for tartrazine. The dye photodegradation process follows a pseudo-first-order kinetic with respect to the Langmuir-Hinshelwood reaction mechanism. A direct dependence between azo dyes degradation rate and chemical structure of dyes has been observed.     

Emerging Light-Harvesting Materials Based on Organic Photovoltaic D/A Heterojunctions for Efficient Photocatalytic Water Splitting

Photocatalytic water splitting to hydrogen is a highly promising method to meet the surging energy consumption globally through the environmentally friendly means. As the initial step before photocatalysis, harvesting photons from sunlight is crucially important, thus making the design of photosensitizers with visible even near-infrared (NIR) absorptions get more and more attentions. In the past three years, organic donor/acceptor (D/A) heterojunctions with absorptions extending to 950 nm, have emerged as the new star light-harvesting materials for photocatalytic water splitting, demonstrating exciting advantages over inorganic materials in solar light utilization, hydrogen yielding rate, etc. This Minireview firstly gives a brief discussion about the principle processes and determining factors for photocatalytic water splitting with organic photovoltaic D/A heterojunction as photosensitizers. Thereafter, the current progress is summarized in details by introducing typical and excellent D/A heterojunction-based photocatalytic systems. Finally, not only the great prospects but also the most challenging issues confronted by organic D/A heterojunctions are indicated along with a perspective on the opportunities and new directions for future material explorations.     

Pd/ZnO和Ag/ZnO复合纳米粒子的制备、表征及光催化活性

 用焙烧前驱物碱式碳酸锌的方法制备了ZnO纳米粒子，采用光还原沉积贵金属的方法制备了Pd／ZnO和Ag／ZnO复合纳米粒子，并利用ICP，XRD，TEM和XPS等测试技术对样品进行了表征，初步探讨了贵金属在ZnO纳米粒子表面形成原子簇的原因．以光催化氧化气相正庚烷为模型反应，考察了样品的光催化活性以及贵金属沉积量对催化剂活性的影响．结果表明：沉积适量的贵金属，ZnO纳米粒子光催化剂的活性大幅度提高．同时，深入探讨了表面沉积贵金属的ZnO纳米粒子光催化剂活性有所提高的内在原因．     

Ternary chalcogenides XGaS2 (X = Ag or Cu) for photocatalytic hydrogen generation from water splitting under irradiation of visible light

Ternary chalcogenide silver gallium sulfide (AgGaS₂), which has an orthorhombic structure, was already synthesized. However, the feasibility of using the crystal for hydrogen production through photocatalytic water splitting has not been explored. Here, we systematically investigated the structural, electronic, optical, and transport properties of XGaS₂ (X = Ag or Cu) with orthorhombic structure by using the first principles calculations. The band alignments indicate that all calculated absolute potentials of the valence and conduction band edges met the requirement of photocatalytic water splitting reaction. The presence of 2.64 and 2.56 eV direct band energy gaps and obvious optical absorption within the visible light range imply that XGaS₂ can correspond to solar light. Moreover, the large electron mobility and the obvious differences between electron mobility and hole mobility were identified in XGaS₂ structures, which is beneficial to the photocatalytic performance of the water splitting reaction. The present findings can provide a helpful reference for developing novel photocatalytic materials with XGaS₂ for hydrogen generation from water splitting under irradiation of visible light.     

Morphology‐controlled Fabrication of SnO2/ZnO Nanocomposites with Enhanced Photocatalytic Performance

In this work, a series of novel SnO₂/ZnO nanocomposites with different morphologies were fabricated via a facile hydrothermal technique followed by calcination in air. The morphological, structural and photocatalytic properties of the SnO₂/ZnO nanocomposites were studied using different methods. The results showed that the synthesized nanocomposites possessed crystal phases of wurtzite hexagonal phase ZnO and tetragonal rutile phase SnO₂. In addition, the morphologies of SnO₂/ZnO nanocomposites strongly depended on the molar ratios of Sn and Zn. Compared with ZnO and SnO₂, the SnO₂/ZnO nanocomposites exhibited considerably higher degradation efficiency for the photodegradation of methylene blue and quinolone antibiotics under mercury lamp irradiation. The SZ‐2 nanospheres exhibited the highest degradation efficiency of 95.81%, which was about 2.63 times higher than that of ZnO nanoparticles. Moreover, the trapping experiments confirmed that ˙OH played the dominant role in MB degradation. Finally, the charge carriers potential transfer pathway and photocatalytic degradation mechanism were put forward. This study provides an economical way to prepare hybrid nanocomposites with controlled morphology for practical applications in the photocatalytic degradation of organic dyes and residual antibiotics.     

Highly efficient visible-light-driven photocatalytic hydrogen production of CdS-cluster-decorated graphene nanosheets

The production of clean and renewable hydrogen through water splitting using photocatalysts has received much attention due to the increasing global energy crises. In this study, a high efficiency of the photocatalytic H(2) production was achieved using graphene nanosheets decorated with CdS clusters as visible-light-driven photocatalysts. The materials were prepared by a solvothermal method in which graphene oxide (GO) served as the support and cadmium acetate (Cd(Ac)(2)) as the CdS precursor. These nanosized composites reach a high H(2)-production rate of 1.12 mmol h(-1) (about 4.87 times higher than that of pure CdS nanoparticles) at graphene content of 1.0 wt % and Pt 0.5 wt % under visible-light irradiation and an apparent quantum efficiency (QE) of 22.5% at wavelength of 420 nm. This high photocatalytic H(2)-production activity is attributed predominantly to the presence of graphene, which serves as an electron collector and transporter to efficiently lengthen the lifetime of the photogenerated charge carriers from CdS nanoparticles. This work highlights the potential application of graphene-based materials in the field of energy conversion.     

Multimetallic Oxynitrides Nanoparticles for a New Generation of Photocatalysts

A versatile synthetic strategy for the preparation of multimetallic oxynitrides has been designed and here exemplarily discussed considering the preparation of nanoscaled zinc–gallium oxynitrides and zinc–gallium–indium oxynitrides, two important photocatalysts of new generation, which proved to be active in key energy related processes from pollutant decomposition to overall water splitting. The synthesis presented here allows the preparation of small nanoparticles (less than 20 nm in average diameter), well-defined in size and shape, yet highly crystalline and with the highest surface area reported so far (up to 80 m² g⁻¹). X-ray diffraction studies show that the final material is not a mixture of single oxides but a distinctive compound. The photocatalytic properties of the oxynitrides have been tested towards the decomposition of an organic dye (as a model reaction for the decomposition of air pollutants), showing better photocatalytic performances than the corresponding pure phases (reaction constant 0.22 h⁻¹), whereas almost no reaction was observed in absence of catalyst or in the dark. The photocatalysts have been also tested for H₂ evolution (semi-reaction of the water splitting process) with results comparable to the best literature values but leaving room for further improvement.     

ZnO/ZnS Heterostructured Nanorod Arrays and Their Efficient Photocatalytic Hydrogen Evolution

Semiconducting heterostructures have been widely applied in photocatalytic hydrogen evolution due to their variable band gaps and high energy conversion efficiency. As typical semiconducting heterostructures, ZnO/ZnS heterostructured nanorod arrays (HNRAs) have been obtained through a simple anion‐exchange process in this work. Structural characterization indicates that the heterostructured nanorods (HNRs) are all composed of hexagonal wurtzite ZnO core and cubic zinc‐blende ZnS shell. As expected, the as‐obtained one‐dimensional heterostructures not only lower the energy barrier but also enhance the separation ability of photogenerated carriers in photocatalytic hydrogen evolution. Through comparisons, it is found that 1D ZnO/ZnS HNRAs exhibit much better performance in photocatalytic hydrogen evolution than 1D ZnO nanorod arrays (NRAs) and 1D ZnS NRAs. The maximum H₂ production is 19.2 mmol h^?1 for 0.05 g catalyst under solar‐simulated light irradiation at 25 °C and the corresponding quantum efficiency is 13.9 %, which goes beyond the economical threshold of photocatalytic hydrogen evolution technology.     

ZnTiO3-TiO2纳米复合材料的光催化性能

通过溶胶 凝胶（Sol-Gel）法制备了ZnTiO3-TiO2纳米复合光催化剂,利用透射电子显微镜、X射线衍射、紫外-可见吸收光谱和ζ电位等测试技术对其形貌、晶体结构及其光谱响应特性进行了表征。 以亚甲基蓝（MB）溶液的脱色降解为模型反应,考察了光源和焙烧温度对该纳米复合材料光催化性能的影响。 结果表明,所得纳米复合材料的催化性能与材料的尺寸、在介质中的分散性能、表面荷电性质等有关。 600 ℃下焙烧3 h所得的ZnTiO3-TiO2纳米复合材料尺寸小（约60 nm）、分散性能好、表面荷负电荷量最高、催化性能最好,且在太阳光下的活性高于紫外光下的。 如太阳光下7 h可使亚甲基蓝（MB）溶液的脱色降解率达到93%,而在紫外光下只有82%;并且其催化活性高于纯TiO2和ZnO的。 该纳米复合催化剂重复使用4次仍能使亚甲基蓝（MB）溶液的脱色降解率在80%以上。 因此,具有较好的光催化稳定性能。     

A Hydrogen Farm Strategy for Scalable Solar Hydrogen Production with Particulate Photocatalysts

Scalable solar hydrogen production by water splitting using particulate photocatalysts is promising for renewable energy utilization. However, photocatalytic overall water splitting is challenging owing to slow water oxidation kinetics, severe reverse reaction, and H₂/O₂ gas separation. Herein, mimicking nature photosynthesis, a practically feasible approach named Hydrogen Farm Project (HFP) is presented, which is composed of solar energy capturing and hydrogen production subsystems integrated by a shuttle ion loop, Fe³⁺/Fe²⁺. Well‐defined BiVO₄ crystals with precisely tuned {110}/{010} facets are ideal photocatalysts to realize the HFP, giving up to 71 % quantum efficiency for photocatalytic water oxidation and full forward reaction with nearly no reverse reaction. An overall solar‐to‐chemical efficiency over 1.9 % and a solar‐to‐hydrogen efficiency exceeding 1.8 % could be achieved. Furthermore, a scalable HFP panel for solar energy storage was demonstrated under sunlight outdoors.     

Catalytic Activity Towards Hydrogen Evolution Dependent of the Degree of Conjugation and Absorption of Six Organic Chromophores

Conjugated materials can, in many cases, absorb visible light because of their delocalized π electron system. Such materials have been widely used as a photoactive layers in organic photovoltaic devices and as photosensitizers in dye-sensitized solar cells. Additionally, these materials have been reported for applications in solar fuel production, working as photocatalysts for the hydrogen evolution reaction (HER). The synthesis of three flexible vinyl groups-containing chromophores is reported. The catalytic activity towards hydrogen evolution of these chromophores has been investigated and compared to their non-vinyl-containing analogues. The catalytic effect was confirmed using two different approaches: electrochemical, using the chromophores to modify a working electrode, and photocatalytic, using the chromophores combined with platinum nanoparticles. A relationship between the degree of conjugation and the catalytic activity of the chromophores has been observed with the electrochemical method, while a relationship between the UV absorption in the solid state and the photocatalytic effect with platinum nanoparticles was observed.     

Photocatalytic water splitting using modified GaN:ZnO solid solution under visible light: long-time operation and regeneration of activity

Overall water splitting using GaN:ZnO solid solution photocatalyst modified with Rh(2-y)Cr(y)O(3) nanoparticles as H(2) evolution cocatalysts under visible light (400 < λ < 500 nm) was examined with respect to long-term durability and regeneration of photocatalytic activity. The rate of visible light water splitting remained unchanged for 3 months (2160 h), producing H(2) and O(2) continuously at a stoichiometric amount. After 6 months of operation, a 50% loss of the initial activity occurred. Regeneration treatment of deactivated catalysts was attempted by reloading the Rh(2-y)Cr(y)O(3) cocatalyst. The degree of activity regeneration depended on the reloading amount. Up to 80% of the initial activity for H(2) evolution could be recovered under optimal treatment conditions. It was also found that deactivation of GaN:ZnO was suppressed to some extent by prior coloading of an O(2) evolution cocatalyst, which helped to suppress oxidative decomposition of GaN:ZnO by valence band holes, thereby improving the durability.     

ZnO/graphene-oxide nanocomposite with remarkably enhanced visible-light-driven photocatalytic performance

In this work, a high-performance photocatalyst of ZnO/graphene-oxide (ZnO/GO) nanocomposite was synthesized via a facile chemical deposition route and used for the photodegradation of organic dye from water under visible light. The nanocomposite was characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller N(2) adsorption-desorption analysis, and UV-Vis diffusion reflectance spectroscopy. The ZnO/GO nanocomposite consisting of flower-like ZnO nanoparticles anchored on graphene-oxide sheets has a high surface area and hierarchical porosity, which is benefit to the adsorption and mass transfer of dye and oxygen species. For the photodegradation of organic dyes under visible light, ZnO/GO nanocomposite exhibited remarkably enhanced photocatalytic efficiency than graphene-oxide sheets and flower-like ZnO particles. Moreover, the photocatalytic efficiency of ZnO/GO nanocomposite could be further improved by annealing the product in N(2) atmosphere. The outstanding photocatalytic performance was ascribed to the efficient photosensitized electron injection and repressed charge carriers recombination in the composite with GO as electron collector and transporter, thus leading to continuous generation of reactive oxygen species for the degradation of methylene blue.