Dispersed ZnO Research Articles

Development of polylactic acid/ZnO composite membranes prepared by ultrasonication and electrospinning for food packaging

In this study, biopolymer-based antimicrobial fibrous membranes constituted by polylactic acid (PLA) and ultrasonically dispersed ZnO nanoparticles (NPs) were developed by electrospinning. The morphology, mechanical properties, thermodynamics and antimicrobial properties of membranes with different ZnO NPs content were comprehensively studied. The results showed that the best performance was achieved when the content of ZnO content was 0.5 wt% (PLA/ZnO-0.5%). Specifically, the tensile strength and elongation at break of the composite membrane were 6.85 ± 0.19 MPa and 74.90 ± 0.59%, respectively, and the inhibition zones of Escherichia coli and Staphylococcus aureus were 15.02 ± 0.18 mm and 14.74 ± 0.06 mm, respectively. In addition, an appropriate ultrasonication time of 45 min improved the thermal, ultraviolet (UV) barrier, and antibacterial properties of the composite membrane. At the 45 min ultrasonication time, the inhibition zone of PLA/ZnO-0.5% against Escherichia coli and Staphylococcus aureus was 18.11 ± 0.15 mm and 15.80 ± 0.11 mm, respectively. Therefore, PLA/ZnO-0.5% can be applied in food packaging to provide an antibacterial effect and UV light barrier.

Nanocellulose-triggered structural and property changes of acrylonitrile-butadiene rubber films

In this study, the effect of cellulose nanocrystals (CNCs) incorporation on the structure–properties of acrylonitrile-butadiene rubber (NBR films), with particular focus on curing enhancement and reinforcing potential, was investigated. The NBR crosslinking efficiency, observed from nuclear magnetic resonance analysis, increased with successive CNC concentration increases due to better dispersion of ZnO from Zn-cellulose complex formation. Energy dispersive X-ray and transmission electron microscope analysis of the films revealed increasingly well-dispersed ZnO with increasing CNC. The increase in the crosslinking density in conjuncture with the reinforcing capability of CNCs resulted in increases in the tensile strength, stiffness, toughness, tear strength and elongation by 203, 8300, 664, 179, and 14%, respectively for films containing 3 phr CNC compared to the neat NBR. The incorporation of 0.5 phr CNC reduced the water absorption of neat CNC by 250%. Overall, water absorption of the nanocomposite films was considerably lower than that of the neat NBR through CNC consolidation of the rubber particles by reducing free volume in the NBR structure. The nanocomposite films show promise for glove and other dipped product applications where improved tear resistance and overall physical properties improvement are needed without compromising the integrity.

Fast photodegradation of rhodamine B and caffeine using ZnO-hydroxyapatite composites under UV-light illumination

Zinc oxide-hydroxyapatite composites were prepared using wet impregnation method. Firstly, a natural phosphate ore rich in silica and calcium phosphate was sieved to separate silica phase from phosphate phase. Then, through a chemical precipitation method, a pure hydroxyapatite (HAP) was obtained, which was used as a support for ZnO immobilization and applied for the photodegradation of two toxic contaminants: a transparent molecule (caffeine) and dye molecule (rhodamine B). During the present work two weight ratio percentages of zinc oxide were used: 25 wt.% and 50 wt.% of ZnO relative to HAP. The samples were characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), X-ray Fluorescence (XRF), BET surface area (SBET), Scanning Electron Microscopy (SEM-EDS) and by Transmission Electron Microscopy (TEM-STEM). The immobilization of ZnO on HAP surface followed by thermal treatment at 400 °C for 2 h to get a homogenous dispersion of ZnO on the hydroxyapatite support. At high ZnO impregnation percentage, photodegradation performances of ZnO-HAP under UV illumination were fast and superior than the ZnO photocatalyst alone. The results showed that due to the presence of HAP, the conversion of both molecules became faster and greater, since it promotes the synergic phenomena of adsorption and photocatalysis. The toxicity of the treated substrate solutions obtained in the corn kernels germination test indicated a low toxicity after the photodegradation processes, probably due to a high mineralization degree.

Improving performance of ZnO flexible dye sensitized solar cell by incorporation of graphene oxide

At today great interest has been paid to hydrogen production by water electrolysis due to their simplicity and low cost. Dye sensitized solar cell are promising devices as renewable electrical power source to achieve water electrolysis because they possess high theoretical efficiency compared with Si based solar cells. In this research, ZnO photo catalyst was modified with graphene oxide (GO) by means of high energy milling. The anode of the flexible dye-sensitized solar cell was fabricated by electrophoretic deposition of the photo catalyst onto flexible electrodes. The obtained materials were characterized by FTIR, XRD, XPS and SEM–EDS. The efficiency and fill factor of ZnO and ZnO–GO cells were estimated from the I–V curve, measured under simulated sunlight. The obtained results demonstrate that ZnO–GO cell have higher efficiency compared with the ZnO cell. The latter can be explained by the better dispersion of ZnO that enlace the dye adsorption onto the fabricated anode and by the presence of GO that improve the absorption of photons from the light.

Zn-promoted Hβ zeolite for gas-phase catalyzed aza-heterocyclic-aromatization of acrolein dimethyl acetal and aniline to quinolines

Catalytic activities of Zn-promoted Hβ zeolite for gas-phase aza-heterocyclic-aromatization of acrolein dimethyl acetal and aniline to quinolines were investigated. the Zn/Hβ catalyst showed better selectivity to quinoline than the parent Hβ one. Characterization results demonstrated that the Zn/Hβ catalyst prepared via deposition precipitation method existed the isolated Zn2+ cations as well as the highly dispersed ZnO clusters, which not only decreased concentration of strong acid sites but also enhanced enhance aromatization process. As a result, the decrease of strong acid sites restrained the cracking of acrolein to acetaldehyde as well as the alkylation of quinoline to ethylquinoline effectively; and the Zn species of catalyst further improved aromatization process of dihydroquinoline to quinoline. Moreover, the Zn/Hβ catalyst presented relatively enhanced ability of anti-activation and excellent regenerability, owing to decrease strong acid-induced polymerization of active intermediates to form the coking. Under the optimized operating conditions, more than 51 % yield of quinoline was achieved over Zn/Hβ catalyst; which far exceeded quinoline yield (28 %) over the pure Hβ one. Besides, a plausible reaction routes in vapor-phase acrolein diethyl acetal with aniline to quinolines were suggested in this paper.

One-pot sonochemical synthesis route for the synthesis of ZnO@TiO2/DW hybrid/composite nanofluid for enhancement of heat transfer in a square heat exchanger

The thermophysical properties of ZnO@TiO2/DW composite nanofluids with (0.1, 0.075, 0.05 and 0.025)mass% concentrations have been experimentally studied. The equal and homogenous dispersion of both ZnO and TiO2 nanoparticles with 50:50 ratio each in distilled water (DW) was attained by the sonochemical method. The efforts are directed to examine the effective thermal conductivity of the different mass% concentrations of ZnO@TiO2/DW composite nanofluid for a selected range of temperatures at 20 to 45 °C. The maximum improvement in thermal conductivity for ZnO@TiO2/DW composite nanofluid was noticed for 0.1 mass% concentration, and the maximum enhancement was spotted 47% higher than the base fluid (DW). The heat transfer properties of ZnO@TiO2/DW composite nanofluids with (0.1, 0.075, 0.05 and 0.025) mass% concentrations and base fluid (DW) in a square heat exchanger were also investigated. Average and local heat transfer values and growth in Nusselt values were conquered for different velocities and corresponding to specific Reynolds numbers range from 4550 to 20,360. The maximum improvement increases about 57% in average heat transfer (h) and Nusselt numbers correspondingly, while local heat transfer for 0.1 mass% is about 500 to 1750 W m−2 K, for 0.075 mass% is 500 to 1500 W m−2 K, for 0.05 mass% is 500 to 1370 and for 0.025 mass% is 500 to 1150 of the composite nanofluid which is greater than base fluid (DW). The ZnO and TiO2 mixture gives the best combination to enhance the overall heat transfer coefficient (h).

Bifunctional ZnO-MgO/activated carbon adsorbents boost H2S room temperature adsorption and catalytic oxidation

A series of bifunctional ZnO-MgO/activated carbon adsorbents (denoted as MgxZn1-x/AC) were synthesized. The molar ratio of Mg/(Mg + Zn) was optimized maintaining a 20 wt. % total content of oxides. The materials were characterized using adsorption of nitrogen, TEM-EDS, XPS, XRD, FT-IR, TG and CO2-TPD. On them an H2S breakthrough capacity was measured in moist and dry conditions in the absence of oxygen in a gas stream. The best adsorbent retained 113.4 mg/g at moist conditions and 96.5 mg/g at dry conditions. Besides a large surface area and pore volume, and a high dispersion of ZnO, the high H2S removal capacity was attributed to MgO, which, owing to its basicity and limited solubility in water, continuously promoted the formation of HS− important for reactive adsorption and then for catalytic oxidation. The detected surface reaction/catalytic oxidation products were ZnS, elemental sulfur and sulfates. Based on the results obtained, plausible desulfurization mechanisms were proposed.

Hydrothermally synthesized zinc oxide nanoparticles for reflectance study onto Si surface

Herein, Zinc Oxide nanoparticles(NPs) are synthesized using hydrothermal method and are used to enhance Si-surface reflectance reduction for enhancing solar cell efficiency with simple and low cost method. The synthesis of ZnO nanorods are optimized by tuning parameters such as stirring time, ultrasonication time and vacuum drying. These NPs shape and size are characterized via XRD, TEM, UV–Visible and PL study. The structural analysis parameters such as preferred orientation, stress in NPs suggest that hydrothermally synthesized ZnO NPs has a problem of particle agglomeration which was resolved with suitable ultrasonication treatment and vacuum drying and the technique is able to produce well dispersed crystalline ZnO nanorods structures along with high aspect ratio. Thereafter, these NPs thin films are fabricated via spin coating onto textured Si surface and then reflectance measurement suggests absorption peak of ZnO in thin film at 370 nm. The reflection study of these NPs thin film are then compared with thin film of NPs synthesized via spray pyrolysis onto textured Si surface and show favourable reflectance reduction for NPs from spray pyrolysis from 15.1% to 11.44% in wavelength region 350–750 nm due to the porous structure. The study suggest that ZnO nanorod structure thin film onto textured Si is able to increase reflectance from existing 14% to 75% in the visible wavelength region 450–750 nm along with significantly decrease reflectance from 25% to 2.5% in wavelength region 350–370 nm.

Effect of dispersed ZnO in Cu–Zn composite oxides on catalytic activity of anisole acetylation

Cu–Zn composite oxide catalysts were prepared by a co-precipitation method and used in the anisole acetylation reaction.

Facile fabrication of ZIF-derived graphene-based 2D Zn/Co oxide hybrid for high-performance supercapacitors

Abstract Recently, rational design and synthesis of two-dimensional (2D) nanoflake based architectures have attracted great attention in energy storage systems due to their unique properties, such as high specific surface area, superior electrical and thermal conductivity. Zeolitic imidazolate frameworks (ZIFs) with 2D structure can be synthesized by a facile aqueous method and be used to obtain 2D metallic/binary metallic oxides. In this paper, graphene oxide and Zn2+ were added in the synthesis of Co-ZIF, and its derived oxide (ZnCoO-G) exhibits 2D nanosheet structure with well dispersed Co3O4 and ZnO nanoparticles after heat treatment. Compared with the derivatives without graphene oxide (ZnCoO) and Zn2+ (CoO-G), ZnCoO-G demonstrates the highest specific capacitance of 711.6 F g−1 at 1 A g−1 with a capacitance retention of 63.6% at 5 A g−1 after 1000 cycles. Also, an asymmetric supercapacitor (ASC) with ZnCoO-G and commercial active carbon as positive and negative electrodes has a maximum energy density of 18.7 W h kg−1 at a power density of 800 W kg−1.

ZnO nanocolumns synthesized by chemical bath process and spray pyrolysis: Ultrasonic and mechanical dispersion of ZnO seeds and their effect on optical and morphological properties

Hexagonal ZnO nanocolumns were synthesized by chemical bath deposition on previously deposited ZnO nanoseeds on Corning glass substrates, at deposition temperatures from 300 to 550 °C in steps of 50 °C, by ultrasonic spray pyrolysis technique. The ZnO nanoseeds were previously suspended in the spraying solution, with and without ultrasonic dispersion. Scanning Electron Microscopy study of surface morphology was carried out revealing the formation of hexagonal ZnO nanocolumns; the smaller diameters were obtained for ZnO seed layers deposited at substrate temperature between 400 and 450 °C. The best vertical alignment was observed on nanocolumns grown from ultrasonic-dispersed ZnO nanoseeds deposited at 400 °C. Raman spectroscopy was used to evaluate the crystal quality of the ZnO nanocolumns, a relationship was determined between nanocolumns stress with a shift to lower wavenumbers of E2H mode, the ZnO seeds deposition temperature and the nanocolumn diameters. Intrinsic defects of ZnO nanocolumns were studied with photo and cathodoluminescence spectroscopy. Also, photoluminescence life time measurements were carried out. Samples grown from ultrasonically dispersed ZnO seeds generated nanocolumns with greater stoichiometry and purity.

Effect of CuO and ZnO Nano-Additives on the Tribological Performance of Paraffin Oil–Based Lithium Grease

The present study investigates the effect on the tribological behavior of paraffin grease incorporated with ZnO and CuO nanoparticles. ZnO nanoparticles of ∼32 nm were synthesized with a precipitation method. X-ray diffraction (XRD), Fourier transform infrared (FTIR), high-resolution scanning electron microscopy (HR-SEM), and energy-dispersive spectroscopy (EDS) were used to characterize the nanoparticles. The grease was formulated with lithium soap (lithium salt of 12-hydroxy stearate) and paraffin oil. The CuO and ZnO nano-additives were blended separately in the paraffin grease in the range between 0.2 to 1.0% w/w. The extreme pressure and antiwear behavior of the CuO and ZnO nano-additive-doped greases were evaluated as per ASTM D2596 and D 2266 respectively using a four-ball tester. Various physical properties of grease samples—for example, drop point, consistency, evaporation loss, water washout, and leakage tendency—were also examined as per ASTM D566, D1403, D1263, D1264, and D972, respectively. The antiwear test results showed that the maximum reduction in mean wear volume (MWV) was obtained (∼36 and ∼56%) with the incorporation of 0.2% w/w of CuO and ZnO nano-additives in the paraffin grease, respectively. At the same concentration, ∼31 and ∼28% decreases in energy consumption were also achieved by the dispersion of ZnO and CuO nano-additives in the paraffin grease. The worn surfaces of the test balls were studied with various analytical tools to determine the wear mechanisms.

MOF-derived yolk-shell Ni@C@ZnO Schottky contact structure for enhanced microwave absorption

Metal–organic frameworks (MOF) derivative used as microwave absorber has been attracting extensive interest due to the diversity of host-guest coordination and unique structure at micro/nano-meters level. However, the accurate adjustment of metal-semiconductor interfaces construct remains a great challenge. Here, a novel hierarchical multi-interfacial Ni@C@ZnO microsphere with special Schottky contact structure was successfully fabricated after annealed the bimetallic Ni-Zn-MOF precursor. The unique yolk-shell microsphere was assembled together by the core-shell Ni@C micro-units and ZnO flakes. The uniformly dispersed ZnO flakes were anchored inside the hierarchical conductive carbon matrix. The yolk-shell Ni@C@ZnO materials displayed high-performance microwave absorption after the micro-nano structure and interfacial design were optimized. In particular, with a low mass additive amount of only 25%, the maximum reflection loss (RL) reached −55.8 dB at 2.5 mm, and the effective absorption bandwidth (RL ≤ −10 dB) covered as wide as 4.1 GHz. The excellent microwave absorption performance could be attributed to the polarized interfaces of Ni-C-ZnO, which contributes a metallic/semiconductor barrier. Thus, both magnetic-dielectric synergetic effect and interfacial polarization might lead to an evident absorption. This novel lightweight magnetic MOF-derived composites promise great potential in the practical microwave absorption fields.

Mn3O4 Nanomaterials Functionalized with Fe2O3 and ZnO: Fabrication, Characterization, and Ammonia Sensing Properties

AbstractThe fabrication of metal oxide‐based gas sensors with tailored structural design is of particular importance for the early recognition of poisonous/explosive analytes like ammonia, an irritating chemical occurring in a plethora of practical contexts. In this regard, the present work reports on the fabrication and gas sensing application of p‐Mn3O4/n‐MxOy nanocomposites with MxOy = Fe2O3 or ZnO. The target systems are developed by chemical vapor deposition of Mn3O4 nanosystems on alumina substrates and subsequent functionalization with iron or zinc oxides by sputtering under mild conditions. Material characterization reveals the formation of high purity composites with a controllable dispersion of Fe2O3 or ZnO into Mn3O4, and a close contact between the single constituents. The latter feature, resulting in the formation of p‐n junctions and in a tailored modulation of Mn3O4 hole accumulation layer, is of strategic importance in obtaining promising responses to ammonia already at moderate temperatures. Furthermore, Fe2O3 or ZnO functionalization empowers the pristine Mn3O4 with good selectivity toward NH3 against other potential interferents. These results, along with the very favorable detection limits, provide new physical insights for the implementation of gas‐sensitive devices with p‐n junctions aimed at practical end uses.

Tuning the ZnO-activated carbon interaction through nitrogen modification for enhancing the H2S removal capacity

Herein, an unusual strategy is reported to enhance the H2S uptake capacity by varying the ZnO-support interaction and controlling the acid-basic environment of the pore channel; this is in place of the generally reported method of decreasing ZnO nanoparticle size and optimizing their porosity. With this regard, coal based activated carbon (AC) is selected as the support and the interaction with ZnO is tuned by introducing N species on AC surface through a soft nitriding strategy. Our strategy is confirmed to be prospective based on the fact that the N-modifying AC supported ZnO adsorbent show a maximum breakthrough sulfur capacity (BSC) of 62.5 mg S/g sorbent, two times larger than that without N-modification (30.5 mg S/g sorbent). The enhanced BSC is attributed to the introduced N species, which not only increases the basicity of the water film condensed in the pores, promoting the dissociation of H2S and H2O, but also influences the electronic structure of ZnO, accelerating the rate of lattice diffusion during in sulfidation process. It is also found that the high BSC of sorbent with N modification is related to the doped N concentrations, ZnO dispersion and the material porosity. This paper provides a new insight for designing supported ZnO based adsorbents.

Nano-ZnO functionalized biochar as a superhydrophobic biosorbent for selective recovery of low-concentration Re(VII) from strong acidic solutions

A novel nano-ZnO functionalized biochar with superhydrophobic surface was successfully synthesized and tested for selective recovery of Re(VII) anions in strong acidic solutions. The as-synthesized biochar was characterized by XRD, XPS, FT-IR, EDX, TEM, STEM-HAADF, SAXS, N2 adsorption-desorption isotherm and water contact angle measurements. The characterization results revealed that the functionalized biochar was composed of highly dispersed ZnO nanoparticles bound to biochar matrix and displayed superhydrophobicity with water contact angle of about 151–156°. Because of the synergistic effect of surface superhydrophobicity and metal affinity, the new biochar exhibited excellent selectivity and high efficiency to Re(VII) in the presence of various competing ions. Adsorption mechanism exploration found that inner-sphere complexation on homogeneous surface would be the dominant interaction, while liquid film diffusion was considered as the rate-controlling step in the sorption process. Due to its excellent selectivity, high efficiency and easy synthesis process, the obtained superhydrophobic biosorbent is ideal candidate for Re(VII) recovery from copper smelting acidic wastewater.

Electrochemistry Studies of Hydrothermally Grown ZnO on 3D-Printed Graphene.

A three-dimensional (3D) printer was utilised for the three-dimensional production of graphene-based pyramids and an efficient hydrothermal procedure for ZnO growth. In particular, the 3D-printed graphene pyramids were forwarded in Pyrex glass bottles with autoclavable screw caps filled with 50 mL of an aqueous solution of zinc nitrate hexahydrate and hexamethylenetetramine for 1 h at 95 °C; sufficient enough time to deposit well-dispersed nanoparticles. X-ray diffraction patterns were in accordance with a Raman analysis and presented the characteristic peaks of graphite along with those of wurtzite ZnO. Different positions on the sample were tested, confirming the uniform dispersion of ZnO on graphene pyramids. From the electrochemical studies, it was found that the charging and discharging processes are affected by the presence of ZnO, indicating one well-defined plateau for each process compared to the previously reported bare graphene pyramids. In total, the material shows a value of 325 mAh g−1, a capacitance retention factor of 92% after 5000 scans, and a coulombic efficiency of 100% for the first scan that drops to 85% for the 5000th scan. This excellent performance is the result of the effect of ZnO and graphene that combines two Li+ accommodation sites, and the contribution of graphene pyramids, which provides more available sites to favor lithium storage capacity. Hence, this anode may be a promising electrode material for lithium-ion batteries.

Uniform zeolitic imidazolate framework coating via in situ recoordination for efficient polysulfide trapping

The “shuttle effect” in lithium sulfur battery system is the most prominent challenge hampering its further development and application in the energy storage industry. Metal-organic framework (MOF) derived carbon materials are considered to be efficient sulfur hosts to confine the polysulfides because of the unique porous structure and the heteroatom doping. However, a strong acid wash step is usually needed to remove the metal or metal oxide residual after pyrolysis, which will produce a large amount of acidic waste solution and increase the complexity of the synthetic process. Herein, instead of being removed, the uniformly dispersed ZnO nanoparticles in the pyrolytic polyhedra from zeolitic imidazolate framework-8 (ZIF-8) is directly used as the metal source to prepare a new ZIF-8 coating layer. This novel structure possesses not only the unique inner porous structure and high conductivity of pyrolytic carbon, but also the extra protection from ZIF-8 layer with both physical confinement and chemisorption to polysulfides. The resulting cathode displays an initial capacity of 1410 mAh g−1 at 0.2 C, and desirable cycling stability and rate capability are also obtained.

Facile synthesis of lightweight carbonized hydrochars decorated with dispersed ZnO nanocrystals and enhanced microwave absorption properties

Application of heterostructures in electromagnetic interference shielding application has been limited by the issue of the uniformly and dispersity of composites. Herein, we synthesized carbonized hydrochars/ZnO nanocrystals (CH/ZnO) composites via a strategy of expanding the interface of heterostructure. The introduction of dispersed ZnO nanocrystals leads to the emergence of the special heterostructure, associated with significant interfacial polarizations, resulting in an upgraded microwave absorption properties. It is demonstrated that the optimized reflection loss can achieve −49.24 dB with the thickness of merely 1.24 mm, and effective bandwidth (less than −10 dB) is ranging from 13.2 GHz to 16.6 GHz. The CH/ZnO composites in this work are outstanding microwave absorber with the merits of lightweight, easy preparation, wide source of raw materials and low cost.

Low-Coordinated Pd Catalysts Supported on Zn1Zr1Ox Composite Oxides for Selective Methanol Steam Reforming

Highly dispersed palladium on nanoscale Zn1Zr1Ox mixed oxides was prepared by incipient wetness impregnation. H2 pretreatment tuned the structure of the catalysts and, hence the catalytic performance in the steam reforming of methanol. Based on catalyst evaluation by XRD, XPS and EXAFS/XANES, it is found that high reduction temperature (400 °C) leads to the formation of PdZnβ alloy, which breaks the Pd-Pd bonds in the metallic Pd phase and forms low-coordinated Pd species in the domain of the metal oxides. These low-coordinated Pd species are responsible for the exclusive selectivity to CO2 as the carbon product. Methyl formate as the reaction intermediate was detected on Pd/Zn1Zr1Ox-R400 catalyst by in situ methanol-DRIFTS and methanol-TPSR, proving the methanol dehydrogenation and coupling reaction pathway on the low-coordinated Pd active sites. The incorporation of ZrO2 facilitates the dispersion of ZnO and Pd species and stabilizes Pd species against growth, with better stability than monometallic palladium. This work effectively shows how to prepare active and selective Pd catalysts for dehydrogenation and steam reformimg of methanol not suffering from the typical poor selectivity of metallic palladium.