Biopolymer Template Research Articles

Sodium Alginate-CuS Nanostructures Synthesized at the Gel-Liquid Interface: An Efficient Photocatalyst for Redox Reaction and Water Remediation.

The use of visible light to propel chemical reactions is an exciting area of study that is crucial in the current socioeconomic environment. However, various photocatalysts have been developed to harness visible light, which consume high energy during synthesis. Thus, synthesizing photocatalysts at gel-liquid interfaces in ambient conditions is of scientific importance. Herein, we report an environmentally benign sodium alginate gel being used as a biopolymer template to synthesize copper sulfide (CuS) nanostructures at the gel-liquid interface. The driving force for the synthesis of CuS nanostructures is varied by changing the pH of the reaction medium (i.e., pH 7.4, 10, and 13) to tailor the morphology of CuS nanostructures. The CuS nanoflakes obtained at pH 7.4 transform into nanocubes when the pH is raised to 10, and the nanostructures deform at the pH of 13. Fourier transform infrared spectroscopy (FTIR) confirms all the characteristic stretching of sodium alginate, whereas the CuS nanostructures are crystallized in a hexagonal crystal system, as revealed by the powder X-ray diffraction analysis. The high-resolution X-ray photoelectron spectroscopy (XPS) spectra show the +2 and -2 oxidation states of copper (Cu) and sulfur (S) ions, respectively. The CuS nanoflakes physisorbed a higher concentration of greenhouse CO2 gas. Owing to a lower band gap of CuS nanoflakes synthesized at a pH of 7.4, compared to other CuS nanostructures prepared at pH 10 and 13, CuS photocatalytically degrades 95% of crystal violet and 98% of methylene blue aqueous dye solutions in 60 and 90 min, respectively, under blue light illumination. Additionally, sodium alginate-copper sulfide (SA-CuS) nanostructures synthesized at a pH of 7.4 demonstrate excellent performance in photoredox reactions to convert ferricyanide to ferrocyanide. The current research opens the door to developing new photocatalytic pathways for a wide range of photochemical reactions involving nanoparticle-impregnated alginate composites prepared on gel interfaces.

Patterns of crystal organization and calcite twin formation in planktonic, rotaliid, foraminifera shells and spines

The foraminiferal order Rotaliida represents one third of the extant genera of foraminifers. The shells of these organisms are extensively used to decipher characteristics of marine ecosystems and global climate events.It was shown that shell calcite of benthic Rotaliida is twinned. We extend our previous work on microstructure and texture characterization of benthic Rotaliida and investigate shell calcite organization for planktonic rotaliid species. Based on results gained from electron backscattered diffraction (EBSD) and field emission electron microscopy (FESEM) imaging of chemically etched/fixed shell surfaces we show for the planktonic species Globigerinoides sacculifer, Pulleniatina obliquiloculata, Orbulina universa (belonging to the two main planktonic, the globigerinid and globorotaliid, clades): very extensive 60°-{001}-twinning of the calcite and describe a new and specific microstructure for the twinned crystals. We address twin and crystal morphology development from nucleation within a biopolymer template (POS) to outermost shell surfaces. We demonstrate that the calcite of the investigated planktonic Rotaliida forms through competitive growth. We complement the structural knowledge gained on the clade 1 and clade 2 species with EBSD results of Globigerinita glutinata and Candeina nitida shells (clade 3 planktonic species). The latter are significantly less twinned and have a different shell calcite microstructure.We demonstrate that the calcite of all rotaliid species is twinned, however, to different degrees. We discuss for the species of the three planktonic clades characteristics of the twinned calcite and of other systematic misorientations. We address the strong functionalization of foraminiferal calcite and indicate how the twinning affects biocalcite material properties.

Synthesis of Nanocrystalline Mg-Al Hydrotalcites in the Presence of Starch-the Effect on Structure and Composition.

The study describes the synthesis of Mg-Al hydrotalcite (Ht) with the use of starch as a structure controlling biotemplate. Syntheses were carried out at room temperature, by co-precipitation at pH = 10. The investigated synthesis parameters included the nature of the precipitating agent (NaOH/Na2CO3 or NH3aq/(NH4)2CO3), the nature of starch (potato, corn and cassava), the method of starch addition to reagents, the method of drying and the effect of washing. The materials were examined with X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy and infrared spectroscopy. The data show that synthesis of Ht materials in the presence of starch, with use of the ammonia-based precipitant, enabled preparation of nanocrystalline Ht with very fine (<50 nm) particle size. All investigated starches had a similar effect on the crystallinity and the grain size of Ht precipitates. Ht with the smallest nanocrystals was obtained when starch was present in all solutions used for synthesis, and the final product subjected to freeze drying. Washing with water was found to enhance recrystallization and exchange of nitrates for carbonates. Infrared spectra showed that an interaction exists between the biopolymer template and the Ht particles, resulting in a higher degree of order within the Ht-adhering starch component.

Konjac glucomannan-templated synthesis of three-dimensional NiO nanostructures assembled from porous NiO nanoplates for gas sensors.

Biopolymer template synthesis has attracted extensive interest for fabricating highly porous metal oxide nanostructures. In this report, a green template-based approach for the synthesis of three-dimensional (3D) NiO nanostructures assembled from porous NiO nanoplates is introduced using a konjac glucomannan (KGM) template. The Ni–KGM composites, which were formed by the immersion of KGM nanofibrils in nickel nitrate solution, were annealed in air at 600 °C to obtain the highly porous NiO nanoplates. The KGM nanofibrils were used as a sacrificial template, which was combusted at a high temperature for the formation of the porous nanostructures. The gas sensor properties of the porous NiO architecture were systematically investigated with four reduced gases including hydrogen sulfide, ammonia, carbon monoxide and hydrogen. The results indicate that the porous NiO nanoplates show a good detection of hydrogen sulfide with a rapid response and recovery speed at low concentrations.

Chitosan reinforced boehmite nanocomposite desiccant: A promising alternative to silica gel

This paper describes the synthesis and performance evaluation of a granular solid desiccant composite synthesized through a sol-gel process at atmospheric pressure and ambient temperature. The composite desiccant essentially comprises of a biopolymer template, chitosan, and nanoscale boehmite particles embedded on the fibrils of the biopolymer. The chitosan fibers not only help in the formation of boehmite nanoparticles but also act as a reinforcing agent and enable the formation of sand like granules upon aging and drying. The composite showed promising ability to dehumidify the moist air. The desiccant was characterized in detail to study its textural, morphological and chemical properties. The results revealed the formation of crystalline, nanostructured composite with moisture adsorption capacity more than its self-weight (>1.5 g/g at 55–65% RH). The high moisture removal capacity, ease of synthesis and scale-up, and green synthesize approach would make the material a sustainable substitute for silica gel.

Bundled-firewood like AlOOH-CaCl2 nanocomposite desiccant

This paper describes a single-step approach to synthesize a nanostructured desiccant essentially consisting of a biopolymer template, metal oxyhydroxide and a lyophilic metal salt at atmospheric pressure and room temperature (30±3°C). The unprecedented ability of the granular desiccant composite to dehumidify air is demonstrated. The composite was characterized in detail with the help of various microscopic and spectroscopic techniques. XRD, ATR-IR and XPS data proved the existence of CaCl2 and nanoscale γ-AlOOH in the composite. FESEM and EDX analyses revealed the formation of the composite with bundled firewood like nanoarchitecture. The composite showed exceptional ability to dehumidify air and the capacity (>2.0g/g) was found to be 5–7 times better than that of commercial silica gel. The solid composite is robust and has the desirable qualities of an ideal desiccant including improved adsorption capacity, low regeneration temperature and eco-friendly nature.

Construction of a Cordyceps sinensis exopolysaccharide-conjugated selenium nanoparticles and enhancement of their antioxidant activities

A Cordyceps sinensis exopolysaccharide (EPS)-conjugated selenium nanoparticles (SeNPs) were successfully constructed through the reduction of SeO32−. The EPS-SeNPs were characterized in terms of formation, morphology, size, Se distribution and phase by UV–vis, FT-IR, transmission electron microscopy (TEM), dynamic light scattering (DLS), energy dispersive X-ray (EDX) and wide angle X-ray diffraction (WAXD) measurements. Results revealed that the SeNPs conjugated to EPS were amorphous and could be well dispersed at a size range of 80–125nm. The interactions between the OH groups of EPS and SeNPs substituted for intermolecular interaction in native EPS to form new CO⋯Se bonds, resulting in good dispersion of SeNPs in the EPS matrix. Besides, the EPS-SeNPs at different Se/P ratios exhibited significant scavenging ability on superoxide anion radical (O2−) and ABTS radical cation (ABTS+) when compared to pure EPS, indicating that the conjugated SeNPs reinforced antioxidant effect of EPS. This work not only provides a simple and efficient way to construct well-dispersed SeNPs in aqueous system, and demonstrates the vital role of the EPS as a biopolymer template for dispersion, stabilization and size control of SeNPs, but also finds the EPS-SeNPs can potentially serve as a good antioxidant towards O2− and ABTS+.

Conversion of Volcanic Tephra to Zeolites for Calcium Ion Cross-Linked Alginate-Zeolite Composites for Enhanced Aqueous Removal of Cu(II) Ions

After alkaline hydrothermal conversion of volcanic tephra to zeolite (VT-Z) particles, calcium ion cross-linked alginate-zeolite composites (VT-Z/CA) were subsequently fabricated as sorbents for enhancing removal of Cu(II) ions from aqueous solution. The naturally occurring VT minerals were used as silica and alumina sources for zeolite crystallization. The conversion conditions were optimized by altering the alkaline concentration, conversion time, temperature and addition of ethanol. After the synthesized VT-Z particles were entrapped into CA biopolymer template, the developed VT-Z/CA composites not only make full use of the excellent adsorption capabilities of zeolites but also prevent the major problems of mobility/agglomeration for zeolite particles in aqueous media. The VT-Z/CA composites were characterized and studied for aqueous removal of Cu(II) ions in a batch mode. Solution pH 5.5 was found to be the best choice. The kinetic data were evaluated by the pseudo-first, pseudo-second order, and Elovich model. The adsorption kinetics followed the pseudo-first model. Langmuir isotherm best described the adsorption behavior with the maximum adsorption capacity for Cu(II) at 121.1 mg g−1 (45 °C). The composites were successfully explored for treatment of Cu(II)-bearing livestock farm wastewater in China. The VT-Z/CA composites offer a highly attractive alternative for remediating heavy metal contaminated water with advantages of being easy to operate, cost-effective, biodegradable, and environmentally benign.

N-doped mesoporous alumina for adsorption of carbon dioxide

N-doped mesoporous alumina has been synthesized using chitosan as the biopolymer template. The adsorbent has been thoroughly investigated for the adsorption of CO2 from a simulated flue gas stream (15% CO2 balanced with N2) and compared with commercially available mesoporous alumina procured from SASOL, Germany. CO2 adsorption was studied under different conditions of pretreatment and adsorption temperature, inlet CO2 concentration and in the presence of oxygen and moisture. The adsorption capacity was determined to be 29.4 mg CO2/g of adsorbent at 55°C. This value was observed to be 4 times higher in comparison to that of commercial mesoporous alumina at a temperature of 55°C. Basicity of alumina surface coupled with the presence of nitrogen in template in synthesized sample is responsible for this enhanced CO2 adsorption. Adsorption capacity for CO2 was retained in the presence of oxygen; however moisture had a deteriorating effect on the adsorption capacity reducing it to nearly half the value.

Alginate as Template in the Preparation of Active Titania Photocatalysts

AbstractA simple and reliable procedure to prepare TiO2 and Au/TiO2 samples with high photocatalytic activity for hydrogen generation from water/methanol mixtures is reported, which uses natural alginate as the templating agent. Aqueous solutions of sodium alginate are flocculated as beads by TiO2+ ions in the presence or absence of AuCl4−. The resulting alginate beads containing approximately 25 wt % of Ti and various Au contents are dehydrated by ethanol washings before drying under supercritical CO2 conditions. The key step in the preparation method is to obtain Au/Ti‐containing alginate aerogels of approximately 700 m2 g−1 Brunauer–Emmett–Teller surface area. The surface area of the TiO2 and Au/TiO2 samples obtained after calcination of the organic biopolymer at 450 °C under air ranges from 187 to 136 m2 g−1, and the Au content has been varied from 1.3 to 0.05 wt % to optimize the photocatalytic activity of the samples. TiO2 forms in the anatase phase according to XRD and Raman spectroscopy. The highest activity Au/TiO2 sample (containing 0.556 wt % of Au) prepared by means of the biopolymer templating method was approximately eight times more active for hydrogen generation using a solar simulator than was an analogous Au‐containing TiO2 P25 sample prepared by means of the conventional deposition–precipitation method.

Biopolymer templated porous TiO2: An efficient catalyst for the conversion of unutilized sugars derived from hemicellulose

An efficient procedure for the conversion of unutilized abundant sugar derivatives, such as d-mannose, d-galactose and lactose, into platform molecule 5-hydroxymethylfurfural in aqueous and organic medium is reported. This process involves biopolymer sodium alginate templated porous TiO2 nanocatalysts containing strong Lewis acidic sites as determined by pyridine-IR and temperature programmed desorption (TPD) of ammonia studies. Porous TiO2 materials were characterized by XRD, SEM, HR-TEM and N2 sorption techniques. Biopolymer templating pathway provided effective synthetic route for the TiO2 nanomaterials, which contain considerable mesoscopic void space as revealed from the HR-TEM and N2 sorption studies. Using this TiO2 catalyst, improved HMF yields were obtained without using expensive ionic liquids as solvents. Hydrothermally obtained TiO2 nanocatalysts showed maximum activity in d-mannose conversion to HMF, whereas nonporous TiO2 is inactive in this reaction. Porosity (surface area), small particle size and strong acidic sites generated through biopolymer templating pathway are crucial for high catalytic activity.

Self-Assembled TiO2 Nanospheres By Using a Biopolymer as a Template and Its Optoelectronic Application

Self-assembled TiO(2) nanoparticulate materials with well-defined spherical morphologies were synthesized by using a biopolymer sodium alginate as a template under different synthesis conditions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) techniques were used to characterize the TiO(2) nanoparticles. N(2) sorption analysis revealed the moderately good surface area (124.0 m(2) g(-1)) and pore volume (0.44 cm(3) g(-1)) of these TiO(2) nanoparticles. The biopolymer templating pathway leads to good-quality self-assembled TiO(2) nanoparticles with dimensions of ca. 10-12 nm within the synthesis temperature range of 0-60 °C. These porous TiO(2) nanomaterials showed high photogenerated current in the presence of a dye (Rose Bengal), used as a sensitizer for several photo on/off cycles.

Efficient Visible-Light Photocatalytic Water Splitting by Minute Amounts of Gold Supported on Nanoparticulate CeO2 Obtained by a Biopolymer Templating Method

Efficient Visible-Light Photocatalytic Water Splitting by Minute Amounts of Gold Supported on Nanoparticulate CeO₂ Obtained by a Biopolymer Templating Method

Efficient Removal of Heavy Metal Ions with Biopolymer Template Synthesized Mesoporous Titania Beads of Hundreds of Micrometers Size

We demonstrated that mesoporous titania beads of uniform size (about 450 μm) and high surface area could be synthesized via an alginate biopolymer template method. These mesoporous titania beads could efficiently remove Cr(VI), Cd(II), Cr(III), Cu(II), and Co(II) ions from simulated wastewater with a facile subsequent solid-liquid separation because of their large sizes. We chose Cr(VI) removal as the case study and found that each gram of these titania beads could remove 6.7 mg of Cr(VI) from simulated wastewater containing 8.0 mg·L(-1) of Cr(VI) at pH = 2.0. The Cr(VI) removal process was found to obey the Langmuir adsorption model and its kinetics followed pseudo-second-order rate equation. The Cr(VI) removal mechanism of titania beads might be attributed to the electrostatic adsorption of Cr(VI) ions in the form of negatively charged HCrO(4)(-) by positively charged TiO(2) beads, accompanying partial reduction of Cr(VI) to Cr(III) by the reductive surface hydroxyl groups on the titania beads. The used titania beads could be recovered with 0.1 mol·L(-1) of NaOH solution. This study provides a promising micro/nanostructured adsorbent with easy solid-liquid separation property for heavy metal ions removal.

Efficient Visible-Light Photocatalytic Water Splitting by Minute Amounts of Gold Supported on Nanoparticulate CeO2 Obtained by a Biopolymer Templating Method

When irradiated with visible light (λ > 400 nm) 1 wt % gold-supported ceria nanoparticles generate oxygen from water (10.5 μmol·h(-1)) more efficiently than the standard WO(3) (1.7 μmol·h(-1)) even under UV irradiation (9.5 μmol·h(-1)). This remarkable photocatalytic activity arises from a novel preparation method to reduce the particle size of ceria (5 nm) by means of electrostatic binding of Ce(4+) to alginate gel, subsequent supercritical CO(2) drying, and calcination. The low loading of Au is crucial for the observed high catalytic activity.

Biopolymer templating as synthetic route to functional metal oxide nanoparticles and porous sponges

The biopolymers dextran and xyloglucan were used to attenuate structural development of a range of metal oxide materials. Dextran was used to prepare catalytic iron, iron–gold, and cerium–copper oxide porous sponges composed of joined nanoparticles. Zinc oxide sponges and nanoparticles coated with <5 nm gold particles were similarly prepared using xyloglucan which was shown to have potential advantages in terms of synthesis properties and cost.

Highly porous and monodisperse magnetic silica beads prepared by a green templating method

We describe the preparation of magnetic silica nanocomposite millimetric beads using alginate as a green biopolymer template. The simple and soft method which is used here is particularly suitable since the alginate template allows a multiscale control of the structure of the material, both its morphological characteristics at the millimetric scale and its porosity at the nanometric level. These nanocomposites are characterised by a high monodispersity, a perfect spherical shape, a very large and multiscale porosity with pore diameters ranging from 2 nm to more than 50 nm, a homogeneous dispersion of the magnetic nanoparticles in the silica matrix and a high magnetic susceptibility which increases linearly with the volume fraction of the nanoparticles. These highly porous materials which can be used as magnetic adsorbents in water treatment, showed a good sorption capacity for methylene blue, chosen as a model dye.

Tuning porphyrin/DNA supramolecular assemblies by competitive binding.

Addition of an intercalating but nonaggregating porphyrin, AuT4, to a preformed adduct between DNA and a strongly aggregating porphyrin, t-H2Pagg, permits control of the extent of aggregation of the latter. The size and the intensity of the ICD and RLS signals depend linearly on the concentration of the intercalating dye and decrease markedly on increasing the concentration of the available binding sites on the biopolymer template.

Defect-Tolerant Single-Electron Charging at Room Temperature in Metal Nanoparticle Decorated Biopolymers

Gold nanoparticles assembled on a biopolymer template (see Figure) between metal electrodes on an insulating substrate are shown to exhibit unambiguous single electron charging effects that are found to depend on the nanoparticle properties and the geometrical contraints imposed by the biopolymer. The results support the idea of using nanoparticles in conjuction with biomolecular organization to produce nanoscale systems with defect-tolerant current–voltage behavior.

Defect-Tolerant Single-Electron Charging at Room Temperature in Metal Nanoparticle Decorated Biopolymers

Gold nanoparticles assembled on a biopolymer template (see Figure) between metal electrodes on an insulating substrate are shown to exhibit unambiguous single electron charging effects that are found to depend on the nanoparticle properties and the geometrical contraints imposed by the biopolymer. The results support the idea of using nanoparticles in conjuction with biomolecular organization to produce nanoscale systems with defect-tolerant current–voltage behavior.