Composite Nanospheres Research Articles

Testing for the Equality of Variance for the Four-parameter Logistic (4PL) Model for the Detection of Vibrio cholerae DNA with Polystyrene-coacrylic Acid Composite Nanospheres

When it comes to finding the best fit of nonlinear curves to acceptable models, linear regression with least squares is the most effective technique. Because residuals (the difference between observed and predicted data) must follow a normal distribution and the data must be free of outliers and uniform variance, statistical tests are used to identify the most appropriate model for a given situation (homoscedasticity). If all of these characteristics are satisfied, the system is said to be robust. In parametric nonlinear regression, one of the numerous assumptions is that the within-group variances of the groups are all the same, which is one of several assumptions (exhibit homoscedasticity). If the variances vary from one another (show heteroscedasticity), then the model is not statistically competent to describe the data as a whole. Data on the detection of Vibrio cholerae DNA with polystyrene-coacrylic acid composite nanospheres as modelled using the nonlinear four-parameter logistic (4PL) regression was preliminary check for homogeneity of variance using the Bartlett’s and Levene’s tests. It was found that the critical value of 2 was 28.869, according to Bartlett's test findings. Excel's CHIDIST function yielded a probability of 0.389 (not significant), suggesting that the variances of the residuals did not change significantly. The p-value for Levenes's test was 0.917, indicating that there were no distinct changes between the residual variances meaning that the use of the 4-PL model in fitting the data was adequate statistically.

Metal organic framework-derived Ni4Mo/MoO2@C composite nanospheres as the sensing materials for hydrogen sulfide detection

Hydrogen sulfide is carcinogenic, corrosive, and flammable, and pathological for most physiological processes. Nevertheless, precise and efficient H2S detection remains challenging. Metal organic framework (MOF) derived metal alloy/oxide nanostructures have been developed recently that show enormous potential and outstanding performance for accurate H2S detection. This paper proposes a new category of MOF derived metal alloy/oxide nanostructures prepared by wet chemical synthesis as plausible H2S gas sensing materials. Compared with pristine sensors, NiMo-MOF sensors exhibit improved H2S gas sensing performance attributed to synergistic effects and large surface areas. NiMo-MOF sensing material achieves the best known gas response for H2S with negligible response to other gas molecules, including HCHO, SO2, C2H5OH, CH3OH, and NH3. Hydrogen sulfide gas response for NiMo-MOF is 3.5 and 2.6 fold higher than bare Ni-MOF and Mo-MOF respectively. The real-time gas response shows that constructed H2S sensor follows an adsorption-oxidation-desorption mechanism and achieved Rg/Ra value is 126 for NiMo-MOF. Thus, the proposed approach provides a mechanism to employ MOF-derived metal alloy/oxide nanostructures as active candidates for improved gas sensing towards effective H2S detection.

Efficient removal of plastic additives by sunlight active titanium dioxide decorated Cd–Mg ferrite nanocomposite: Green synthesis, kinetics and photoactivity

Large use of flame retardants or additives in plastic industries have caused scientific attention as their leaching from consumer products is indicative of environmental concern. Moreover, plastic additives have proven features of endocrine disruptors, genotoxicity and persistence. Therefore, photodegradation of tetrabromobisphenol A (TBBPA) and bisphenol A (BPA) were explored in water. Seeing environmental safety, titanium dioxide decorated magnesium substituted cadmium ferrite (CdMgFe2O4@TiO2) was synthesized by using plant extract of M. koenigii via co-precipitation. Sharp peaks obtained in PXRD ensured high crystallinity and purity of distorted spherical nanocomposite (5–25 nm). Subsequently, CdMgFe2O4@TiO2 nanocatalyst was evaluated for the effective elimination of plastic additives at variable reaction parameters (pollutant: 2–10 mgL-1; catalyst: 5–25 mg; pH: 3–7, dark-sunlight). With 20 mg of catalytic dose, CdMgFe2O4@TiO2 showed maximum degradation of 2 mgL−1 of TBBPA (91%) and BPA (94%) at neutral pH under sunlight. Considerable reduction in persistence of TBBPA (t1/2:2.4 h) and BPA (t1/2:2.1 h) indicated admirable photoactivity of CdMgFe2O4@TiO2. Results were supported by BET, zeta potential, band reflectance and photoluminescence analysis that indicated for higher surface area (90 m2g-1), larger particle stability (−20 mV), lower band gap (1.9 eV) and inhibited charge-pairs recombination in nanocomposite. Degradation consisted of initial Langmuir-adsorption followed by first order kinetics. Scavenger analysis revealed the role of hydroxyl radical in photodegradation studies. Nanocomposite was effective up to eight cycles without any significant loss of activity that advocated its high-sustainability and cost-effectiveness. Overall, with excellent surface characteristics, green synthesized CdMgFe2O4@TiO2 nanocomposite is a promising and alternative photocatalyst for industrial applications.

Self-Assembled Silver Nanoparticles Decorated on Exfoliated Graphitic Carbon Nitride/Carbon Sphere Nanocomposites as a Novel Catalyst for Catalytic Reduction of Cr(VI) to Cr(III) from Wastewater and Reuse for Photocatalytic Applications.

Silver nanoparticles decorated on an exfoliated graphitic carbon nitride/carbon sphere (AgNP/Eg-C3N4/CS) nanocomposites were synthesized by an adsorption method with a self-assembled process. These nanoparticles were characterized by different techniques like UV–visible (UV–vis) spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), thermal gravimetric analysis (TGA), Raman spectroscopy, scanning electron spectroscopy (SEM), transmission electron spectroscopy (TEM), electrochemical impedance spectroscopy (EIS), and ζ potential. AgNP/Eg-C3N4/CS nanocomposites showed a higher catalytic reduction activity for the conversion of Cr(VI) into Cr(III) with formic acid (FA) at 45 °C when compared to bulk graphitic carbon nitride (Bg-C3N4, Eg-C3N4, CS, and Eg-C3N4/CS). The kinetic rate constants were determined as a function of catalyst dosage, concentration of Cr(VI), pH, and temperature for the AgNP/Eg-C3N4/CS nanocomposite. This material showed higher reduction efficiency (98.5%, k = 0.0621 min–1) with turnover frequency (0.0158 min–1) for the reduction of Cr(VI) to Cr(III). It also showed great selectivity and high stability after six repeated cycles (98.5%). Further, the reusability of the Cr(III)-AgNP/Eg-C3N4/CS nanocomposite was also investigated for the photocatalytic degradation of methylene blue (MB) under visible light irradiation with various time intervals and it showed good degradation efficiency (α = 97.95%). From these results, the AgNP/Eg-C3N4/CS nanocomposite demonstrated higher catalytic activity, improved environmental friendliness, lower cost for the conversion of toxic Cr(VI) to Cr(III) in solutions, and also good reusability.

Investigation of the potassium‐ion storage mechanism of nickel selenide materials and rational design of nickel selenide‐C yolk‐shell structure for enhancing electrochemical properties

Metal selenide is contemplated as expeditious anode material for potassium-ion batteries (KIBs). Here, nickel selenide (NiSe2-Ni0.85Se) was investigated as an anode material for KIBs. The NiSex transformed into K2Se and K2Se3 (K2Sex) and reversibly returned to NiSex after the discharge and charge processes (17NiSe2 + 3Ni0.85Se + 38 K+ + 38e− ↔ 19.55Ni + 10K2Se + 9K2Se3). Furthermore, to enhance the electrochemical properties of nickel selenide, yolk-shell-structured nickel selenide and hollow carbon nanosphere composites, in which nickel selenides intensively existed in the core and were partially formed into nanocrystals in the shell, were produced by simple salt-infiltration and a post-treatment. NiSex@C exhibited improved cycle and rate properties compared to bare NiSex because of its structural merits that led to stable cycle performance and high electrochemical kinetics. NiSex@C exhibited 373 mA h g−1 for the 100th cycle at 0.05 A g−1 and 234 mA h g−1 at 1.0 A g−1.

Ultralong lifetime room-temperature phosphorescence in aqueous medium from silica confined polymer carbon dots for autoluminescence-free bioimaging and multilevel information encryption

Ultralong room-temperature phosphorescence (URTP) materials have innate superiority in eliminating autoluminescence for bioimaging, but achieving URTP in aqueous medium is a highly challenging task, especially for carbon dot-based materials. Here we present a facile one-step hydrothermal method to effectively promote RTP emission in an aqueous medium by confining polymer carbon dots (PCDs) in silica nanospheres (SNSs) with tetraethylorthosilicate as only raw material. The polymer carbon dots-silica nanosphere composites (PCDs-SNSs) exhibit ultralong lifetime up to 2.19 s (nearly 9 s to naked eye) at ambient temperature and atmosphere. To the best of our knowledge, this is the longest RTP lifetime of carbon dot-based materials in aqueous media to date. As indicated, RTP should originate from the subfluorescent CO groups. The shielding of SNSs to all kinds of quenching in the confined space in which there are strong interactions between PCDs and SNSs, e.g, covalent bond and hydrogen bond, which enhances the rigidity of cross-linked framework and protects emitting centers from non-radiative deactive processes of triplet state, is the main reason for the URTP observed in aqueous media. Besides, the PCDs-SNSs solution exhibits outstanding stability and low cytotoxicity. Based on the distinctive properties in aqueous media, the PCDs-SNSs have been successfully used as autoluminescence-free probes for bioimaging with high sensitivity and signal-to-noise ratio, and as security ink for strong concealment and moisture-related multilevel information protection.

Composites of NiSe2@C hollow nanospheres wrapped with Ti3C2Tx MXene for synergistic enhanced sodium storage

Sodium-ion batteries (SIBs) have the virtues of abundant sodium source and low price, but the serious volume expansion and poor cycle stability caused by the large sodium ion radius limit its practical application. Herein, we develop a three-dimensional (3D) Ti3C2Tx MXene wrapped NiSe2@C hollow nanospheres (NiSe2@C@MXene) composites for advanced sodium ion storage. The electrostatic self-assembly of MXene on NiSe2@C hollow nanospheres not only provides dual structural confinement on carbon coated NiSe2, but also efficiently inhibits the self-stacking of MXene. Taking advantage of the highly conductive 3D hierarchical network, the NiSe2@C@MXene electrode is endowed with enhanced electrochemical activity, fast electrochemical dynamic and abundant spatially confined active sites, leading to high reversibility and stable structural integration. Consequently, the NiSe2@C@MXene electrode provides a synergistic enhanced capacity of 327 mA h g−1 at 2000 mA g−1 after 4000 cycles, indicating high-rate capability and long-term stability. This work provides a new route toward developing MXene engineered Ni-based electrode materials for high-performance sodium storage.

Application of a Catechol-Polyamine Co-Deposition method for synthesis of Heteroatom-Doped carbon nanomaterials

Mussel-inspired chemistry, based on dopamine and its derivatives, has attracted widespread attention in the past decade. However, dopamine and its derivatives are expensive and the modification process requires a large amount of buffer solution, which greatly hinder their large-scale application. Here, a simple, versatile and cost-effective catechol-polyamine (Cat-amine) co-deposition method, which has excellent conformal coating performance independent of the composition, dimension, and shape of the substrate, has been developed. The co-deposition takes place in water, and the thickness of the resultant conformal Cat-amine polymer coating can be precisely tailored. In addition, due to the elemental composition of the as-prepared Cat-amine coating is adjustable, N doped or N, S co-doped carbon frameworks with various shapes can be easily prepared. As representative examples, yolk-shell structured nanospheres with nickel silicate inside the hollow N doped carbon nanospheres have been prepared. The composite nanospheres exhibit excellent cycle stability and superior rate capability when evaluated as anode materials for lithium-ion batteries. This highly reproducible and scalable approach provides new ideas for the large-scale preparation of advanced carbon nanocomposites.

One-pot solvothermal preparation of graphene encapsulated SnO nanospheres composites for enhanced lithium storage

SnO based material is one of the most promising anode materials for lithium-ion batteries owing to its high theoretical capacity. However, the difficult synthesis process, large volume expansion and rapid capacity decay, etc., limited its further application. Herein, graphene encapsulated SnO nanospheres, self-assembled from numerous nano-sized secondary nanoparticles, have been successfully synthesized through an efficient one-pot solvothermal method within three hours. The graphene encapsulation and secondary particle assembly structure effectively improves the conductivity of SnO, shortens the ion transmission path and reduces its volume expansion during cycling, thus achieving cycle stability. SnO/G-3 H composite delivers a discharge capacity of 1307 mA h g −1 after 700 cycles at 800 mA g −1 , and maintained an enhanced rate capability of 423 mA h g −1 at 3000 mA g −1 . This simple, economic, and environmental-friendly synthesis route can be extended to the preparation of other transition metal oxide materials.

Fe/Co-Loaded Hollow Carbon Sphere Nanocomposites as Excellent Cathodic Catalysts of Zn-Air Battery

The development of an efficient, stable and low-cost cathode catalyst is necessary for the practical application of Zn-air batteries. In this paper, Fe3+/Co2+ ions were in situ incorporated into polydopamine during the polymerization of dopamine on the surface of the SiO2 spheres. After subsequent pyrolysis and leaching SiO2, the products loaded with different metals (NHCS-Fe, NHCS-Co, NHCS-Fe1Co0.6, NHCS-Fe1Co4, NHCS-Fe1Co10) were obtained. The samples possess a typical hollow carbon sphere (HCS) structure and show efficient oxygen reduction reaction (ORR) performance under neutral and alkaline conditions. Especially in the neutral electrolyte, the NHCS-Fe exhibits the comparable electrochemical catalytic activity to the commercial Pt/C. For NHCS-Fe, its ORR half-wave potential in neutral and alkaline media is 0.78 V and 0.83 V respectively. Corresponding neutral Zn-air battery reveals a maximum power density of 118.8 mW·cm−2, while they are respective 0.82 V and 46.99 mW·cm−2 for Pt/C. Alkaline Zn-air battery with NHCS-Fe releases a maximum power density of 262.4 mW·cm−2, displaying superior performance to Pt/C. Our work is instructive for the synthesis of novel ORR catalysts with outstanding activity by a versatile synthesis strategy.

Revealing the Hemispherical Shielding Effect of SiO2@Ag Composite Nanospheres to Improve the Surface Enhanced Raman Scattering Performance.

Many studies widely used SiO2@Ag composite nanospheres for surface enhanced Raman scattering (SERS), which mainly contributes to electromagnetic enhancement. In addition to experiments, previous simulations mostly adopted a two-dimensional model in SERS research, resulting in the three-dimensional information being folded and masked. In this paper, we adopted the three-dimensional model to simulate the electric field distribution of SiO2@Ag composite nanospheres. It is found that when the Ag nanoparticles are distributed densely on the surface of SiO2 nanospheres, light cannot pass through the upper hemisphere due to the local surface plasmon resonance (LSPR) of the Ag nanoparticles, resulting in the upper hemisphere shielding effect; and if there are no Ag nanoparticles distributed densely on the surface of SiO2 nanospheres, the strong LSPR cannot be formed, so the incident light will be guided downward through the whispering gallery mode of the spherical structure. At the same time, we designed relevant experiments to synthesize SiO2@Ag composite nanosphere as SERS substrate and used Rhodamine 6G as a probe molecule to study its SERS performance. This design achieved a significant SERS effect, and is very consistent with our simulation results.

Reduced toxicity of protein/magnetic targeted drug delivery system for improved skin cancer treatment in mice model

Skin cancer is one of the most common types of cancers. Although majority of skin cancers can be treated effectively if they are diagnosed at an early stage, delayed treatment for some types, such as melanoma, are life threatening. This current study evaluated the therapeutic effects of a recently developed targeted drug delivery system (DDS) to treat an experimental skin squamous cell carcinoma (SCC) in a mouse model. This DDS can release drugs into the body at a designated rate and location. The system consists of biodegradable polymer microspheres of encapsulated magnetic nanoparticles, human albumin, and 5-fluorouracil (5-FU). While the magnetic forces keep the nanocomposite spheres in the targeted cancer area, the protein promotes increased absorption of the DDS near cancer cells to release the therapeutic agent. While tumor sizes were significantly decreased and cancer tissue underwent dramatic necrosis, no remote organ and lymph node metastasis were observed. The tissue specimens collected from vital organs (lungs, liver, kidneys, and lymph nodes adjcent to the cancer sites) were histologically examined and did not showobvious damages and adverse tissue responses after the DDS injections. Overall, this study confirmed that this DDS is successful in treating cancer without toxic effects and may be a possible alternative to traditional therapies.

Novel MnO2-CuO-BaO metal oxide nanocomposite for high performance supercapacitors

Novel MnO2-CuO-BaO (MCB) spherical nanocomposite was synthesized by facile hydrothermal method at 80 °C from aqueous solutions. The sample was primarily characterized by Powder X-ray Diffraction, Scanning Electron Microscopy and Dynamic Light scattering measurements. XRD showed the existence of MnO2, CuO and BaO in crystalline form with average crystallite size 16 nm. SEM and DLS studies demonstrated a wide particle size distribution. Cyclic voltammetry (CV) and electrochemical impedance (EIS) measurements were recorded to examine the electrochemical characteristics. CV profile revealed a pseudocapacitance behavior of the nanocomposite. A noticeably high specific capacitance of 198 F/g was established at a scan rate of 10 mV/sec in aqueous 1 M KOH electrolyte. This strongly suggested Mn-Cu-Ba mixed metal oxide nanocomposite as a promising electrode material in supercapacitor technology.

Interconnected magnetic carbon@NixCo1-xFe2O4 nanospheres with core–shell structure: An efficient and thin electromagnetic wave absorber

The applications of cobalt ferrite and nickel ferrite composite materials on electromagnetic (EM) wave absorption are the research hotspot currently. However, the systematical comparison study between these two ferrites composites have rarely been carried out. Thus, the EM wave absorption performance of interconnected carbon@NixCo1-xFe2O4 composites with core–shell structures were investigated comprehensively in this work. A series of magnetic nanospheres including NiFe2O4, cobalt-doped nickel ferrite, nickel–cobalt ferrite, nickel-doped cobalt ferrite and CoFe2O4 were synthesized firstly, and then uniformly encapsulation by carbon rendered the corresponding C@NixCo1-xFe2O4 composites nanospheres. Synthesis reactions involved for C@NixCo1-xFe2O4 formation were investigated in detail, and afterwards their magnetic behavior, EM wave absorption performance and absorbing mechanism were thoroughly explored and analyzed. Results show that when nickel is dominant element and cobalt is doping element (Ni0.75Co0.25Fe2O4), the composite nanosphere exhibits optimum EM wave absorption performance. When the sample thickness is just 1.9 mm, its RLmin value can reach −51 dB, and the corresponding EAB width is 3.3 GHz. The synthesized C@Ni0.75Co0.25Fe2O4 can be qualified as an efficient and thin electromagnetic wave absorber, which is mainly attributed to its special structure, fair electromagnetic matching and impedance matching.

A novel ratiometric fluorescence nanoprobe for sensitive determination of uric acid based on CD@ZIF-CuNC nanocomposites.

Anovel ratiometric fluorescence nanoprobe based on carbon dots (CDs) and Cu nanoclusters (CuNCs) was designed for the label-free determination of uric acid (UA). The metal-organic framework (MOF) encapsulated CuNCs (ZIF-CuNC), and nitrogen-doped CDs can self-assemble into well-defined spherical nanocomposites (CD@ZIF-CuNC) due to physical adsorption. Under the excitation wavelength of 360nm, the CD@ZIF-CuNC nanocomposites exhibit two evident intrinsic emissions peaked at 460nm (CDs) and 620nm (ZIF-CuNC), respectively. In the presence of H2O2, the fluorescence of CD@ZIF-CuNC at 620nm is quenched remarkably within 1min, while little effect on the emission at 460nm is observed. Therefore, taking the fluorescence at 620nm as the report signal and 460nm as the reference signal, ratiometric quantitative determination of H2O2 was achieved withalinear range of 1-100μM and adetection limit of 0.30μM. The CD@ZIF-CuNC nanoprobe was successfully applied tothe determination of UA that is catalyzed by uricase to produce H2O2, obtaining the linear range of 1-30μM and the detection limit of 0.33μM. Eventually, this strategy has been successfully applied to the determination of UA in human urine samples. A novel and convenient CDs@ZIF-CuNCs-based nanoplatform was constructed for sensitive ratiometric fluorescence determinationof UA.

Enhanced Antibacterial and Anti-Biofilm Activities of Antimicrobial Peptides Modified Silver Nanoparticles.

BackgroundThe biofilms could protect bacteria from antibiotics and promote the production of drug-resistant strains, making the bacteria more difficult to be eradicated. Thus, we developed an AMP@PDA@AgNPs nanocomposite, which is formed by modifying silver nanoparticles (AgNPs) with antimicrobial peptides (AMP) modified nanocomposite to destroy biofilm in this study.MethodsThe AMP@PDA@AgNPs nanocomposite was prepared with polymerization method and characterized by using ultraviolet-visible (UV-vis) spectroscopy, dynamic light scattering (DLS), Fourier transform-infrared spectroscopy (FT-IR), and transmission electron microscope (TEM). The antibacterial effects of the nanocomposite were investigated by using agar diffusion method and minimum inhibitory concentration (MIC) test. The quantitative analysis of the biofilm formation by the nanocomposite was conducted using crystal violet staining and confocal laser scanning microscope (CLSM).ResultsThe DLS and TEM analysis showed it was a spherical nanocomposite with 200 nm size and well dispersed . The results of UV-vis and FT-IR confirmed the presence of AMP and AgNPs. The nanocomposite had an excellent biocompatibility at 100 μg/mL. And the AMP@PDA@AgNPs nanocomposite showed superior antimicrobial activity against both Gram-negative (E. coli, P. aeruginosa) and Gram-positive (S. aureus) bacteria than AgNPs or AMP. Importantly, the mRNA expression of biofilm-related genes were decreased under the action of the nanocomposites.ConclusionAn AMP@PDA@AgNPs nanocomposite with good biocompatibility was successfully prepared. The nanocomposite could destruct bacterial biofilms by inhibiting the expression of biofilm-related genes. The synergistic strategy of AMPs and AgNPs could provide a new perspective for the treatment of bacterial infection.

Composite Nanospheres Comprising Luminescent Carbon Dots Incorporated into a Polyhedral Oligomeric Silsesquioxane Matrix

Composite Nanospheres Comprising Luminescent Carbon Dots Incorporated into a Polyhedral Oligomeric Silsesquioxane Matrix

Novel PVA-Based Microspheres Co-Loaded with Photothermal Transforming Agent and Chemotherapeutic for Colorectal Cancer Treatment.

Background: We previously designed an electrospinning chitosan (CS) nanofiber-based carrier, using polyvinyl alcohol (PVA) as an adjuvant to deliver doxorubicin (DOX) and MoS2 nanosheets for postoperative tumor re-occurrence inhibition. However, owing to that the nanofibrous mat is un-injectable, this composite nanofiber is far from being clinically applicable. Materials and Methods: Via modulating the electrospray parameters, polyvinyl alcohol (PVA) beads string doped with DOX and MoS2 (PVA/MoS2/DOX microspheres) were prepared, which were further crosslinked with glutaraldehyde to obtain the water-stability. Results: Under the 808-nm laser irradiation, MoS2 nanosheets rendered the prepared PVA/MoS2/DOX microspheres an excellent light-to-heat conversion performance with η of 23.2%. Besides, the heat generated by near-infrared laser irradiation can improve the effect of chemotherapy by promoting the release rate of DOX. HT29 cell and tumor-bearing nude mice were used to systematically study the combined tumor treatment efficiency of composite nanospheres. Conclusion: PVA/MoS2/DOX nanospheres have excellent photothermal effect and chemotherapy effect, which can completely suppress the tumor recurrence. Therefore, the PVA/MoS2/DOX nanospheres are anticipated to find potential applications in the treatment of local colorectal cancer.

Preparation of chitosan-modified magnetic Schiff base network composite nanospheres for effective enrichment and detection of hippuric acid and 4-methyl hippuric acid

Chitosan-modified magnetic Schiff base network composite nanospheres (Fe3O4@SNW@Chitosan) were prepared for the enrichment and detection of hippuric acid (HA) and 4-methyl hippuric acid (4-MHA) via magnetic solid phase extraction (MSPE) connected with HPLC. The SNW was one of the covalent organic framework, which constructed through covalent bonds, shown comprising solvent stability, low density and accessible pores. The obtained Fe3O4@SNW@Chitosan has many merits as a magnetic sorbent, including a hydrophilic surface, uniform pore size, unique ordered channel structure, and superparamagnetism. The favourable linearity of this MSPE-HPLC method was in the range of 1-1000 μg L−1, and LODs of HA and 4-MHA were 0.3 μg L−1 and 0.2 μg L−1, respectively. The recoveries in urine samples were range from 95.3 to 109.0 % with the RSD less than 9.6 %. When employed for the enrichment of HA and 4-MHA, Fe3O4@SNW@Chitosan exhibited great potential as a candidate for preconcentration.

Maghemite/ZnO nanocomposites: A highly efficient, reusable and non-noble metal catalyst for reduction of 4-nitrophenol

Maghemite/ZnO nanocomposites synthesized by a two step process were used for catalytic reduction of p-nitrophenol. Maghemite nanoparticles were synthesized by hydrothermal technique followed by deposition of ZnO on it via co-precipitation process. X-ray diffraction analysis suggested formation of Maghemite and ZnO with tetragonal and hexagonal close packed structure respectively whereas electron microscopy images indicated the formation of near spherical nanocomposites with a size range of 30–50 nm. Maghemite/ZnO calcined at 300 °C is investigated as heterogeneous catalyst for reduction of p-nitrophenol and its catalytic activity is compared with that of Maghemite and ZnO nanoparticles. The parameters responsible for reduction of p-nitrophenol over Maghemite/ZnO were scrutinized using Response Surface Methodologyand the predicted values of reduction efficiency were found to be in a good agreement with the experimental findings (R2 > 0.9). The highest achievable percentage of reduction of target molecular species was noted to be of 98.6%. Optimization study showed that maximum reduction efficiency was observed at optimum conditions: p-NP concentration = 0.2 mM, Maghemite/ZnO loading = 200 ppm, reaction time = 6 min. Maghemite/ZnO has shown noticeably higher catalytic activity than pure oxides which remained almost unaltered for five consecutive cycling suggesting possible commercial potential of the developed material.