Tahereh Jafari

Photocatalytic Water Splitting—The Untamed Dream: A Review of Recent Advances

Photocatalytic water splitting using sunlight is a promising technology capable of providing high energy yield without pollutant byproducts. Herein, we review various aspects of this technology including chemical reactions, physiochemical conditions and photocatalyst types such as metal oxides, sulfides, nitrides, nanocomposites, and doped materials followed by recent advances in computational modeling of photoactive materials. As the best-known catalyst for photocatalytic hydrogen and oxygen evolution, TiO2 is discussed in a separate section, along with its challenges such as the wide band gap, large overpotential for hydrogen evolution, and rapid recombination of produced electron-hole pairs. Various approaches are addressed to overcome these shortcomings, such as doping with different elements, heterojunction catalysts, noble metal deposition, and surface modification. Development of a photocatalytic corrosion resistant, visible light absorbing, defect-tuned material with small particle size is the key to complete the sunlight to hydrogen cycle efficiently. Computational studies have opened new avenues to understand and predict the electronic density of states and band structure of advanced materials and could pave the way for the rational design of efficient photocatalysts for water splitting. Future directions are focused on developing innovative junction architectures, novel synthesis methods and optimizing the existing active materials to enhance charge transfer, visible light absorption, reducing the gas evolution overpotential and maintaining chemical and physical stability.

Superhydrophobic and stable mesoporous polymeric adsorbent for siloxane removal: D4 super-adsorbent

Synthesis of a new class of siloxane adsorbent (D4) was done to purify methane-rich gases including biogas and digester gas, at near ambient temperature and atmospheric pressure. The nanoporous polymeric adsorbent with controlled wettability was successfully prepared under solvothermal conditions. Imidazole groups were introduced into the samples by copolymerization of divinylbenzene (DVB) with 1-vinylimidazole (VI). The copolymer composition was varied to obtain optimum adsorption performance. Low-cost PDVB and PDVB-VI were evaluated under different adsorption conditions with a gas flow rate of 10 mL min−1. To simulate near real time biogas composition, 50%-relative humidity at 25 °C was maintained to assess the effect of humidity on D4 removal efficiency. In addition, the mixture gas was used to evaluate the adsorptive activity in the presence of CO2 (up to 35%). While PDVB alone demonstrates a significant adsorption activity with a capacity of 1951 ± 74 mg g−1, an improvement in adsorption capacity to 2370 ± 92 mg g−1, was noted with PDVB-VI. Characterization of exhausted adsorbent demonstrates the correlation between D4 adsorption and PDVB-VI-x textural properties. Finally, PDVB-VI-x was readily regenerated after five cycles with less than 10% loss in adsorption activity under both dry and humid conditions.

Modified Mesoporous Silica for Efficient Siloxane Capture.

In this study, octamethylcyclotetrasiloxane (D4) was removed by using a novel modified solid adsorbent of mesoporous silica. The adsorbent was synthesized using inverse micelles with some modifications in the synthesis process (temperature of gelation) and in the post treatment conditions (calcination temperature and heating rate) with a concomitant improvement of D4 uptake. This is the first report on regulating the textural properties of the mesoporous silica material UCT-14 to develop an active silica adsorbent. These adjustments resulted in an increase of the silica surface area from 391 to 798 m(2)·g(-1), which leads to a high capacity (686 mg·g(-1)) of D4-capture for the silica synthesized at 80 °C, calcined at 450 °C with the heating rate of 100 °C·min(-1) (Si-Syn80). This adsorbent showed comparable adsorption performance with the widely used commercial silica gel under dry and humid condition. Recyclability tests on the commercial silica gel and mesoporous silica synthesized at 120 °C and calcined at 450 °C with a heating rate of 100 °C·min(-1) (called Si-Syn120 or Si-450 or Si-100 °C·min(-1)) indicated that the Si-Syn120 (capacity drop 10%) is more efficient than silica gel (capacity drop 15%) after three cycles. Although, the presence of moisture (25%) in the nitrogen gas stream led to capacity reduction in both Si-Syn120 and commercial silica gel, the modified UCT-14 shows slightly better resistance to humid condition.

Hydrophobic mesoporous adsorbent based on cyclic amine–divinylbenzene copolymer for highly efficient siloxane removal

This paper presents a new class of octamethylcyclotetrasiloxane (D4 siloxane) adsorbent based on the copolymer of divinylbenzene and a novel methacrylate monomer. The novel cyclic amine based methacrylate monomer was synthesized employing click chemistry and was polymerized to form a mesoporous adsorbent under solvothermal conditions and tested for siloxane removal. The D4 adsorption capacity of the novel adsorbent is 2220 mg g−1, which is greater than the adsorption capacities of mesoporous poly(divinylbenzene) and commercial activated charcoal. The adsorbent retains 47% regeneration capacity after 10 usage cycles. The high specific adsorption is due to a combination of physisorption, caused by the mesoporosity and pore volume and chemisorption, as evidenced by spectroscopic results. The incorporation of functional groups into a mesoporous structure with significantly enhanced specific adsorption offers future opportunities towards tailored polymer properties for efficient industrial applications in siloxane removal.

Hierarchical Mesoporous NiO/MnO2@PANI Core–Shell Microspheres, Highly Efficient and Stable Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions

We report on the new facile synthesis of mesoporous NiO/MnO2 in one step by modifying inverse micelle templated UCT (University of Connecticut) methods. The catalyst shows excellent electrocatalytic activity and stability for both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline media after further coating with polyaniline (PANI). For electrochemical performance, the optimized catalyst exhibits a potential gap, ΔE, of 0.75 V to achieve a current of 10 mA cm-2 for the OER and -3 mA cm-2 for the ORR in 0.1 M KOH solution. Extensive characterization methods were applied to investigate the structure-property of the catalyst for correlations with activity (e.g., XRD, BET, SEM, HRTEM, FIB-TEM, XPS, TGA, and Raman). The high electrocatalytic activity of the catalyst closely relates to the good electrical conductivity of PANI, accessible mesoporous structure, high surface area, as well as the synergistic effect of the specific core-shell structure. This work opens a new avenue for the rational design of core-shell structure catalysts for energy conversion and storage applications.

Chapter 11 – Cancer Therapy

Over the last two decades, iron oxide nanoparticles have demonstrated great progress and potential for use in oncological medicine. Due to their overall utility for a vast number of applications, iron oxides have been extensively investigated. This type of nanoparticle has numerous desirable properties such as facile synthesis, ease of functionalization, favorable magnetic characteristics, and biocompatible and biodegradable and is generally considered safe. Cancer therapy has already benefited in a number areas from the use of iron oxide nanoparticles in such areas as cancer imaging, a variety of therapeutic approaches including immunotherapy, cell tracking and monitoring, improved efficacy, and safety. While several forms of magnetite-based nanoparticle formulations are FDA approved as either magnetic resonance imaging (MRI) contrast agents or iron-deficiency therapeutics, there are still a number of other applications that these nanoparticles can be used for. Iron oxide nanoparticles can come in a number of shapes, sizes, and composition and can have modifiable coatings with targeting molecules such as antibodies, peptides, and small molecules. These surface moieties can improve tumor-targeting capabilities, while the nanoparticle itself can allow for monitoring by MRI and even optical methods depending on the modifications used and intended applications. Other potential cancer applications include improved delivery of cancer therapeutics, magnetic hypothermia, photothermal ablation, personalized medicine approaches, and photodynamic therapy. These approaches can result in multifunctional and/or theranostic nanoparticles suitable for diagnosis, treatment, and treatment monitoring of cancer.

Synthesis of Large Mesoporous–Macroporous and High Pore Volume, Mixed Crystallographic Phase Manganese Oxide, Mn2O3/Mn3O4 Sponge

The controlled synthesis of mixed crystallographic phase Mn2O3/Mn3O4 sponge material by varying heating rates and isothermal segments provides valuable information about the morphological and physical properties of the obtained sample. The well-characterized Mn2O3/Mn3O4 sponge and applicability of difference in reactivity of H2 and CO2 desorbed during the synthesis provide new developments in the synthesis of metal oxide materials with unique morphological and surface properties. We report the preparation of a Mn2O3/Mn3O4 sponge using a metal nitrate salt, water, and Dextran, a biopolymer consisting of glucose monomers. The Mn2O3/Mn3O4 sponge prepared at 1 °C·min-1 heating rate to 500 °C and held isothermally for 1 h consisted of large mesopores-macropores (25.5 nm, pore diameter) and a pore volume of 0.413 mL/g. Furthermore, the prepared Mn2O3/Mn3O4 and 5 mol %-Fe-Mn2O3/Mn3O4 sponges provide potential avenues in the development of solid-state catalyst materials for alcohol and amine oxidation reactions.

Synthesis and Electrocatalytic Activity of Ammonium Nickel Phosphate, [NH4]NiPO4·6H2O, and β-Nickel Pyrophosphate, β-Ni2P2O7: Catalysts for Electrocatalytic Decomposition of Urea

Electrocatalytic decomposition of urea for the production of hydrogen, H2, for clean energy applications, such as in fuel cells, has several potential advantages such as reducing carbon emissions in the energy sector and environmental applications to remove urea from animal and human waste facilities. The study and development of new catalyst materials containing nickel metal, the active site for urea decomposition, is a critical aspect of research in inorganic and materials chemistry. We report the synthesis and application of [NH4]NiPO4·6H2O and β-Ni2P2O7 using in situ prepared [NH4]2HPO4. The [NH4]NiPO4·6H2O is calcined at varying temperatures and tested for electrocatalytic decomposition of urea. Our results indicate that [NH4]NiPO4·6H2O calcined at 300 °C with an amorphous crystal structure and, for the first time applied for urea electrocatalytic decomposition, had the greatest reported electroactive surface area (ESA) of 142 cm2/mg and an onset potential of 0.33 V (SCE) and was stable over a 24-h test period.

Partial Oxidation of Methane to Synthesis Gas Using Supported Ga‐Containing Bimetallic Catalysts and a Ti‐Promoter

A series of bimetallic Ga‐containing materials using TiO2 and TiO2‐promoted SiO2 supports have been prepared. Rhodium, palladium, and platinum have been used as additional metals in this system. The materials are characterized and used as catalysts for the partial oxidation of methane into synthesis gas (H2 and CO). The presence of a low quantity of titanium in the form of anatase TiO2 was shown to improve the overall activity of catalytic methane oxidation and to strongly increase the selectivity of partial oxidation products over the total oxidation of methane to carbon dioxide and water. Particular attention is paid to the formation of gallium‐metal alloys on the surface of the catalyst supports. Rh‐Ga‐Ti‐SiO2 was found to be the most active and selective catalyst, giving 89 % conversion of methane and 99 % selectivity to synthesis gas at 750 °C, as well as exhibiting catalytic activity and preferential conversion to partial oxidation products at temperatures as low as 350 °C.

Studies of the Hierarchical Structure in UCT Manganese Oxides

In a recent report from our group, inverse micelles were used as the soft template in the synthesis of wellordered mesoporous manganese oxide using a sol-gel-based method. The materials synthesized using this method are known as University of Connecticut (UCT) mesoporous materials. UCT materials are formed in an acidic mixture that consists of a defined ratio of hydrotropic ion precursor, metal precursor, interface modifier, and surfactant. The surfactant molecules form inverse micelles, which encapsulate the reagents during the synthesis process. These features serve as uniformly sized nano-reactors within which hydrolysis and condensation of oxo-clusters occurs. Upon calcination, highly monodisperse nanoparticles will form within the inverse micelles, and the subsequent packing of these nanoparticles during aggregation leads to monodisperse meso-pores defined by intra-particle voids. The surfactant and hydrotropic nitrate ions in this process play key roles in controlling aggregation and condensation of oxoclusters. Moreover, by modifying the ratio of the components in the mixture, and the process conditions with respect to the chosen metal precursor, this method can be used to synthesize mesoporous oxide materials from across the periodic table, including transition metals and non-metals [1-4].