Coprecipitation and hydrothermal synthesis of CaO from dolomite in the presence of Sapindus rarak extract for biodiesel production: catalysts characterization and optimization.

High-purity CaO cubic crystallites extracted from limestone exhibited excellent activity as base catalysts for waste cooking oil (WCO) conversion into biodiesel. Saponin from Sapindus rarak extract acted as a surfactant in CaO extraction and transformation into well-defined cubic microcrystallites. The application of saponin from Sapindus rarak extract as a surfactant for CaO production results in a high level of CaO purity and particle size reduction compared to directly calcined limestone (CaO-MgO). The catalytic activity was evaluated on CaO from hydrothermal and co-precipitation synthesis, MgO and CaO-MgO derived from limestone, giving hydrothermal CaO catalysts enhanced biodiesel yield. Optimization of transesterification conditions using Box Behnken Design response surface methodology achieved 92.40% biodiesel yield at 65 °C, 3 h reaction time and when using 5% of CaO catalysts.

The role of pH-induced tautomerism of polyvinylpyrrolidone on the size, stability, and antioxidant and antibacterial activities of silver nanoparticles synthesized using microwave radiation.

Tautomerism alters the structure and properties of materials, which can be exploited to control their chemical and biological activities. The role of pH-induced tautomerism of polyvinylpyrrolidone (PVP) was determined by measuring the size, stability, and antioxidant and antibacterial properties of microwave synthesized-silver nanoparticles (AgNPs). TEM and XRD analyses confirmed the formation of face-centered cubic silver nanoparticles. PVP stabilized the AgNPs by interaction with the carbonyl or hydroxyl groups depending on the tautomerization under different pH conditions. At pH 4, PVP was stable in the keto tautomer, stabilizing Ag through electron donation of oxygen atoms in the carbonyl group, producing smaller AgNPs with a higher zeta potential. At pH 7 and 9, the enol tautomer PVP stabilized the AgNPs via oxygen atoms in the hydroxyl group, forming large nanoparticles. The keto form of PVP improved the stability and antioxidant and antibacterial properties of AgNPs compared with the enol form. This study also excluded the antioxidant contribution of PVP via hydrogen donation to free radicals. A facile method for controlling the size of AgNPs by adapting the pH-induced tautomerism of PVP that affects their stability and antioxidant and antibacterial activities is thus reported.

Microwave-assisted synthesis of silver nanoparticles as a colorimetric sensor for hydrogen peroxide.

To consider silver nanoparticles (AgNPs) as a colorimetric sensor for H2O2 we require investigation of the effects of the homogeneity of the nanoparticle size and morphology on the sensor parameters. Uniformly-sized Ag nanoparticles with diameters of ∼18.8 ± 2.8 nm were produced using microwave irradiation (AgNP1) but non-uniform particles with diameters of ∼71.2 ± 19.4 nm (AgNP2) were formed without microwave irradiation. Microwave synthesis produced AgNP1 with superiority in terms of repeatability, selectivity and sensor stability for up to eight months of storage over AgNP2. AgNP1 exhibited higher sensitivity and detection limits in the working range of 0.01-40000 µM as compared to AgNP2. The application of the AgNP sensor to milk samples provided recovery values of 99.09-100.56% for AgNP1 and 98.18-101.90% for AgNP2. Microwave irradiation resulted in strong and uniform PVP-Ag interactions for isotropic growth into small nanoparticles. Size and morphology uniformity determined the characteristics of the AgNP sensor that can be applied for H2O2 detection in a wide range of concentrations and real-time evaluation, with the potential for industrial applications.

Direct synthesis of Fe-aluminosilicates from red mud for catalytic deoxygenation of waste cooking oil.

Conversion of red mud (RM) that contains a high level of silica, alumina and iron minerals into heterogenous catalysts, offers a route for the utilization of abundant toxic by-products of bauxite refining. In this study, the conversion of red mud into mesoporous Fe-aluminosilicate produced selective catalysts for the deoxygenation of waste cooking oil to green diesel hydrocarbons. Direct conversion of red mud in the presence cetyltrimethylammonium bromide into Fe-aluminosilicate (RM-CTA) produced a highly mesoporous structure with oligomeric Fe2O3 clusters within the pores. When red mud was treated with citric acid (RM-CA-CTA), a wide distribution of Fe2O3 particles was obtained on the aluminosilicate external surface. TEM analysis showed a well-defined hexagonal mesoporosity of Fe-aluminosilicate obtained from untreated red mud, while the treated red mud produced lower regularity mesopores. RM-CTA exhibits 60% WCO conversion and 83.72% selectivity towards liquid products with 80.44% diesel hydrocarbon (C11-C18) yield. The high selectivity was due to the high acidity of Fe-aluminosilicate to dissociate the C-O bond and the regularity of mesostructure for efficient hydrocarbon diffusion, preventing a cracking reaction.

Synthesis of mesoporous zeolite Y using Sapindus rarak extract as natural organic surfactant for deoxygenation of Reutealis trisperma oil to biofuel.

Saponin is a plant-derived chemical with an amphiphilic glycoconjugate structure extracted from sapindaceae plants like Sapindus rarak. This study investigated saponin extract of Sapindus rarak as a natural template for formation of mesoporous zeolite Y. Surface area and mesoporosity of zeolite Y were improved with optimization of Sapindus rarak extract (SRE) concentration (Y-Ln; n = 2, 5, 10 or 15 mL), reaching 216.26 m2 mesoporous area and 0.214 cm3 g-1 mesoporous volume for Y-L10 samples. A different loading of Ni was impregnated onto Y-L10 zeolite to improve Lewis/Brønsted acidity as catalysts in the deoxygenation of Reutealis trisperma oil (RTO) into hydrocarbon fuels. Impregnating 15% Ni on NaY zeolite enhanced Lewis acidity to 0.4556 mmol g-1, producing 48.8% liquid oil with 85.43% degree of deoxygenation. A high selectivity towards C15 and C17 hydrocarbon was analyzed from liquid yield, indicating the contributing factor from Lewis acidity and mesoporosity to enhance deoxygenation and prevent the hydrocracking reaction.

Optimization of hierarchical ZSM-5 structure from kaolin as catalysts for biofuel production.

Optimization of hierarchical ZSM-5 structure by variation of the first hydrothermal step at different times provides insight into the evolution of micro/mesopores and its effect as a catalyst for deoxygenation reaction. The degree of tetrapropylammonium hydroxide (TPAOH) incorporation as an MFI structure directing agent and N-cetyl-N,N,N-trimethylammonium bromide (CTAB) as a mesoporogen was monitored to understand the effect towards pore formation. Amorphous aluminosilicate without the framework-bound TPAOH achieved within 1.5 h of hydrothermal treatment provides flexibility to incorporate CTAB for forming well-defined mesoporous structures. Further incorporation of TPAOH within the restrained ZSM-5 framework reduces the flexibility of aluminosilicate gel to interact with CTAB to form mesopores. The optimized hierarchical ZSM-5 was obtained by allowing hydrothermal condensation at 3 h, in which the synergy between the readily formed ZSM-5 crystallites and the amorphous aluminosilicate generates the proximity between micropores and mesopores. A high acidity and micro/mesoporous synergy obtained after 3 h exhibit 71.6% diesel hydrocarbon selectivity because of the improved diffusion of reactant within the hierarchical structures.

Hydrothermal effect of gunningite use Pluronic F127-Gelatin as template and the ibuprofen adsorption performance.

The gunningite has been successfully synthesized using Pluronic F127 and gelatin as template via hydrothermal at 100-200 °C for 12-48 h. By scanning electron microscopy, nitrogen adsorption-desorption, and X-ray diffraction, changes in structure, pore size, and morphology due to ibuprofen adsorption were investigated in gunningite. Various hydrothermal (temperature and time) parameters had an influence on the percentage elimination (%) of ibuprofens. Gunningite's specific surface area intensifies from 14.60 to 24.03 m2/g as the longer hydrothermal time. In batch adsorption studies, the resulting sample was conducted to isotherm and kinetic analysis to evaluate the distribution of ibuprofen between the liquid and solid phases. Pseudo-first-order kinetics with an adsorption capacity range of 27-34.5 mg g-1 were the best fit for the observed data. Consequently, gunningite may be considered a viable adsorbent for the large-scale treatment of water contaminated with ibuprofen and related anti-inflammatory medicines.

Hectorite-CTAB-alginate composite beads for water treatment: kinetic, isothermal and thermodynamic studies.

Encapsulation of hectorite-modified CTAB with Ca-alginate formed reusable adsorbent beads for wastewater treatment. The thermogravimetric analysis (TGA) investigation indicated excellent thermal stability results for BHec-40 compared to Hec-40. Although the mesoporous surface area of BHec-40 decreased to 79.74 m2 g-1 compared to 224.21 m2 g-1 for Hec-40, the hectorite-CTAB-alginate beads showed high adsorption capacity and stability for methyl orange (MO) adsorption with more than 60% removal after five adsorption-desorption cycles. The influence of pH (3-11), temperature (30, 40, and 50 °C), initial concentration (50-400 mg L-1), and contact time were studied to obtain the kinetics and thermodynamics of adsorption. The outcomes revealed a maximum monolayer adsorption capacity of 117.71 mg g-1 for BHec-40. The kinetics of adsorption demonstrated the suitability of using the pseudo-first-order kinetic model, while the equilibrium adsorption data follows the Langmuir isotherm. Thermodynamic analysis indicates physisorption of MO onto BHec-40. BHec-40 improves the reusability as an adsorbent for the removal of anionic dyes from aqueous media.

The effect of gelatin as pore expander in green synthesis mesoporous silica for methylene blue adsorption.

Mesoporous silica NSG had been synthesized while employing gelatin as a natural template to successfully increase the particle size and expand the pore diameter of NSG. All silica samples exhibited a similar XRD pattern with a broad peak centred at 2θ = 22.9°, as the characteristic of amorphous silica. FTIR results showed that the reduction of Si-O-Si symmetric stretching vibrations at 1075 cm-1 was due to the use of a high percentage of gelatin. Moreover, TEM analysis displayed the mesoporous channels in the form of a honeycomb structure with a diameter of ± 6 nm. Gelatin enhanced the surface area of silica from 467 to 510 m2/g, the pore volume from 0.64 to 0.72 cc/g and expanded the pore diameter from 3.5 nm to 6.0 nm. The expansion of the ordered mesopores with the increase of P123: gelatin ratios was elucidated by the pore size distribution. The adsorption capacity of methylene blue (MB) was improved on mesoporous silica with an expanded pore dimension to give 168 mg/g adsorption capacity within 70 min.

Fast Removal of Methylene Blue via Adsorption-Photodegradation on TiO2/SBA-15 Synthesized by Slow Calcination.

TiO2/SBA-15 photocatalysts were successfully prepared by impregnating low loading titania to SBA-15 via slow calcination. The photocatalyst is efficient for fast methylene blue removal via adsorption and photodegradation methods. The impregnation of low TiO2 loading via slow calcination enhanced TiO2 dispersion that preserved the SBA-15 porosity and uniform morphology. High interfacial interaction of TiO2/SBA-15 improves TiO2 photoresponse by narrowing the bandgap, resulting in a stronger redox ability. The methylene blue removal on 10%TiO2/SBA-15 followed the pseudo-second-order kinetic model that reached 67% removal efficiency in 90 min. The synergy between adsorption and photodegradation is responsible for the fast methylene blue removal. These results indicate the importance of maintaining the adsorption capacity in SBA-15 after impregnation with TiO2 for efficient adsorption-photodegradation processes, which can be achieved by controlling the deposition of TiO2 on SBA-15. A low titania loading further reduced the cost of photocatalysts, thus becoming a potential material for environmental pollution treatment.

Controlling the Size and Porosity of Sodalite Nanoparticles from Indonesian Kaolin for Pb2+ Removal.

Mesoporous sodalite nanoparticles were directly synthesized from Indonesian kaolin with the addition of CTABr as a mesopore template. The studies highlighted the importance of aging time (3-12 h) and temperature (50-80 °C) on increasing surface area and mesoporosity of sodalite. Indonesian kaolin was used without pre-treatment and transformed to sodalite following the initial molar composition of 10 Na2O: 2 SiO2: Al2O3: 128 H2O. Characterization data revealed the formation of high surface area sodalite with mesoporosity at increasing aging temperatures and times. The presence of CTABr as templates produced sodalites nanoparticles with smaller aggregates than the non-template sodalite. The sodalite sample obtained at 80 °C of crystallization temperature for 9 h (S80H9) displayed the highest mesopore volume (0.07612 cm3/g) and the highest adsorption capacity of Pb2+ (212.24 mg/g). Pb2+ was suggested to adsorb via ion exchange with the Na+ counter cation and physical adsorption.

Uniform rod and spherical nanocrystalline celluloses from hydrolysis of industrial pepper waste (Piper nigrum L.) using organic acid and inorganic acid.

Conversion of lignocellulosic biowastes from agricultural industry into nanocrystalline cellulose provides pathway to reduce environmental pollution while enhancing the economic value of biowastes. Nanocellulose (NCC) with uniform morphology was isolated from pepper (Piper nigrum L.) stalk waste (PW) using acid hydrolysis method. The role of inorganic acids (sulfuric acid, hydrochloric acid, phosphoric acid), organic acids (oxalic acid, citric acid, acetic acid) and variation of sonication times were investigated on the physicochemical characteristics, self-assembled structure, crystallinity, particle size, zeta potential and thermal stability of the isolated nanocellulose. Hydrolysis using inorganic acids transformed cellulose from PW into a spherical shaped NCC at ~33-67 nm of average diameter. Meanwhile hydrolysis in organic acids produced rod-shaped NCC at 210-321 nm in length. This study highlighted the role of acidity strength for organic acid and inorganic acid in controlling the level of hydrogen bond dissociation and the dissolution of amorphous fragments, which consequently directing the morphology and the physicochemical properties of NCCs.

Green Synthesis of Hexagonal Hematite (α-Fe2O3) Flakes Using Pluronic F127-Gelatin Template for Adsorption and Photodegradation of Ibuprofen.

Hematite (α-Fe2O3) with uniform hexagonal flake morphology has been successfully synthesized using a combination of gelatin as natural template with F127 via hydrothermal method. The resulting hematite was investigated as adsorbent and photocatalyst for removal of ibuprofen as pharmaceutical waste. Hexagonal flake-like hematite was obtained following calcination at 500 °C with the average size was measured at 1-3 µm. Increasing the calcination temperature to 700 °C transformed the uniform hexagonal structure into cubic shape morphology. Hematite also showed high thermal stability with increasing the calcination temperatures; however, the surface area was reduced from 47 m2/g to 9 m2/g. FTIR analysis further confirmed the formation Fe-O-Fe bonds, and the main constituent elements of Fe and O were observed in EDX analysis for all samples. α-Fe2O3 samples have an average adsorption capacity of 55-25.5 mg/g at 12-22% of removal efficiency when used as adsorbent for ibuprofen. The adsorption capacity was reduced as the calcination temperatures increased due to the reduction of available surface area of the hexagonal flakes after transforming into cubes. Photocatalytic degradation of ibuprofen using hematite flakes achieved 50% removal efficiency; meanwhile, combination of adsorption and photocatalytic degradation further removed 80% of ibuprofen in water/hexane mixtures.

Identification of C2-C5 products from CO2 hydrogenation over PdZn/TiO2-ZSM-5 hybrid catalysts.

The combination of a methanol synthesis catalyst and a solid acid catalyst opens the possibility to obtain olefins or paraffins directly from CO2 and H2 in one step. In this work several PdZn/TiO2-ZSM-5 hybrid catalysts were employed under CO2 hydrogenation conditions (240-360 °C, 20 bar, CO2/N2/H2 = 1 : 1 : 3) for the synthesis of CH3OH, consecutive dehydration to dimethyl ether and further oxygenate conversion to hydrocarbons. No significant changes after 36 h reaction on the methanol synthesis catalyst (PdZn/TiO2) were observed by XRD, XAS or XPS. No olefins were observed, indicating that light olefins undergo further hydrogenation under the reaction conditions, yielding the corresponding alkanes. Increasing the aluminium sites in the zeolites (Si : Al ratio 80 : 1, 50 : 1 and 23 : 1) led to a higher concentration of mild Brønsted acid sites, promoting hydrocarbon chain growth.

Utilization of red mud waste into mesoporous ZSM-5 for methylene blue adsorption-desorption studies.

Red mud as industrial waste from bauxite was utilized as a precursor for the synthesis of mesoporous ZSM-5. A high concentration of iron oxide in red mud was successfully removed using alkali fusion treatment. Mesoporous ZSM-5 was synthesized using cetyltrimethylammonium bromide (CTABr) as a template via dual-hydrothermal method, and the effect of crystallization time was investigated towards the formation of mesopores. Characterization using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicated the formation of cubic crystallite ZSM-5 with high surface area and mesopore volume within 6 h of crystallization. Increasing the crystallization time revealed the evolution of highly crystalline ZSM-5; however, the surface area and mesoporosity were significantly reduced. The effect of mesoporosity was investigated on the adsorption of methylene blue (MB). Kinetic and thermodynamic analysis of MB adsorption on mesoporous ZSM-5 was carried out at a variation of adsorption parameters such as the concentration of MB solution, the temperatures of solution, and the amount of adsorbent. Finally, methanol, 1-butanol, acetone, hydrochloric acid (HCl), and acetonitrile were used as desorbing agents to investigate the reusability and stability of mesoporous ZSM-5 as an adsorbent for MB removal.

Enhanced CO2 methanation at mild temperature on Ni/zeolite from kaolin: effect of metal-support interface.

Catalytic CO2 hydrogenation to CH4 offers a viable route for CO2 conversion into carbon feedstock. The research aimed to enhance CO2 conversion at low temperature and to increase the stability of Ni catalysts using zeolite as a support. NaZSM-5 (MFI), NaA (LTA), NaY (FAU), and NaBEA (BEA) synthesized from kaolin were impregnated with 15% Ni nanoparticles in order to elucidate the effect of surface area, porosity and basicity of the zeolite in increasing Ni activity at mild temperature of ∼200 °C. A highly dispersed Ni catalyst was produced on high surface area NaY meanwhile the mesoporosity of ZSM-5 has no significant effect in improving Ni dispersion. However, the important role of zeolite mesoporosity was observed on the stability of the catalyst. Premature deactivation of Ni/NaA within 10 h was due to the relatively small micropore size that restricted the CO2 diffusion, meanwhile Ni/NaZSM-5 with a large mesopore size exhibited catalytic stability for 40 h of reaction. Zeolite NaY enhanced Ni activity at 200 °C to give 21% conversion with 100% CH4 selectivity. In situ FTIR analysis showed the formation of hydrogen carbonate species and formate intermediates at low temperatures on Ni/NaY, which implied the efficiency of electron transfer from the basic sites of NaY during CO2 reduction. The combination of Ni/NaY interfacial interaction and NaY surface basicity promoted CO2 methanation reaction at low temperature.

Lewis acid Ni/Al-MCM-41 catalysts for H2-free deoxygenation of Reutealis trisperma oil to biofuels.

The activity of mesoporous Al-MCM-41 for deoxygenation of Reutealis trisperma oil (RTO) was enhanced via modification with NiO nanoparticles. Deoxygenation at atmospheric pressure and under H2 free conditions required acid catalysts to ensure the removal of the oxygenated fragments in triglycerides to form liquid hydrocarbons. NiO at different weight loadings was impregnated onto Al-MCM-41 and the changes of Lewis/Brønsted acidity and mesoporosity of the catalysts were investigated. The activity of Al-MCM-41 was enhanced when impregnated with NiO due to the increase of Lewis acidity originating from NiO nanoparticles and the mesoporosity of Al-MCM-41. Increasing the NiO loading enhanced the Lewis acidity but not Brønsted acidity, leading to a higher conversion towards liquid hydrocarbon yield. Impregnation with 10% of NiO on Al-MCM-41 increased the conversion of RTO to hydrocarbons via the deoxygenation pathway and reduced the products from cracking reaction, consequently enhancing the green diesel (C11-C18) hydrocarbon products.

Barium promoted Ni/Sm2O3 catalysts for enhanced CO2 methanation.

Low temperature CO2 methanation is a favorable pathway to achieve high selectivity to methane while increasing the stability of the catalysts. A Ba promoted Ni/Sm2O3 catalyst was investigated for CO2 methanation at atmospheric pressure with the temperature ranging from 200-450 °C. 5Ni-5Ba/Sm2O3 showed significant enhancement of CO2 conversion particularly at temperatures ≤ 300 °C compared to Ni/Sm2O3. Incorporation of Ba into 5Ni/Sm2O3 improved the basicity of the catalysts and transformed the morphology of Sm2O3 from random structure into uniform groundnut shape nanoparticles. The uniformity of Sm2O3 created interparticle porosity that may be responsible for efficient heat transfer during a long catalytic reaction. Ba is also postulated to catalyze oxygen vacancy formation on Sm2O3 under a reducing environment presumably via isomorphic substitution. The disappearance of a high temperature (∼600 °C) reduction peak in H2-TPR analysis revealed the reducibility of NiO following impregnation with Ba. However, further increasing the Ba loading to 15% formed BaNiO3-BaNiO2.36 phases which consequently reduced the activity of the Ni-Ba/Sm2O3 catalyst at low temperature. Ni was suggested to segregate from BaNiO3-BaNiO2.36 at high temperature thus exhibiting comparable activity with Ni/Sm2O3 at 450 °C.

Size tunable mesoporous carbon microspheres using Pluronic F127 and gelatin as co-template for removal of ibuprofen.

Size tunable mesoporous carbon microspheres, MCMs were obtained using Pluronic F127 and gelatin in co-templating method via hydrothermal and pyrolysis treatments. The presence of gelatin increased the mechanical strength of Pluronic F127 which can sustain the uniform microspherical structure of carbon following pyrolysis at 950 °C. The diameter of MCMs were controlled by variation of weight ratios between Pluronic F127 to gelatin from 1:0.01 to 1:1. MCMs exhibited inter-particulate mesoporous structure with high thermal stability (<500 °C). The MCMs were used as adsorbent for removal of ibuprofen and the kinetic studies using linear regression analysis revealed the adsorption fits pseudo second-order kinetic. The rate of adsorption and the amount of adsorbed ibuprofen were correlated well with the surface area and the crystallite size of MCMs. The efficiencies of ibuprofen adsorption on MCMs were also investigated when ibuprofen was dissolved at different concentration of water and hexane mixtures, the effect temperature variation and the amount MCMs to the volume of ibuprofen solution.

Pd local structure and size correlations to the activity of Pd/TiO2 for photocatalytic reforming of methanol.

The interaction between Pd and TiO2 for promoting photocatalytic activity was investigated by tailoring the size of Pd nanoparticles and monitoring the photocatalytic activity of methanol photo-reforming reaction for hydrogen gas production. We show that at 0.6 wt% Pd loading, the catalyst with highly dispersed nanoparticles obtained at 1 °C temperature exhibits superior photocatalytic activity for hydrogen gas production. At different weights of Pd loading, tailoring two sets of catalysts with different structural properties provides correlation between the changes in the Pd local structures and the rate of hydrogen production. The impact of controlling the structural properties of metal nanoparticles on influencing H2 production outweighs the effect of metal loading variation. The differences of Pd/TiO2 activity at the different metal loadings were correlated with the changes in the Pd local structure consequently affecting the electronic transfer and photocatalytic efficiency.