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Ammonium hydroxide

About: Ammonium hydroxide is a(n) research topic. Over the lifetime, 3943 publication(s) have been published within this topic receiving 40777 citation(s).


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TL;DR: Corn stover was pretreated with aqueous ammonia in a flow-through column reactor, a process termed ammonia recycled percolation (ARP), and the enzymatic digestibility was related with the removal of lignin and hemicellulose, perhaps due to increased surface area and porosity.
Abstract: Corn stover was pretreated with aqueous ammonia in a flow-through column reactor, a process termed ammonia recycled percolation (ARP). This method was highly effective in delignifying of the biomass, reducing the lignin content by 70-85%. Most lignin removal occurred within the first 20 min of the process. Lignin removal by ARP was further confirmed by FTIR analysis and lignin staining. The ARP process solubilized 40-60% of the hemicellulose but left the cellulose intact. The solubilized carbohydrate existed in oligomeric form. Carbohydrate decomposition during the pretreatment was insignificant. Corn stover treated for 90 min exhibited enzymatic digestibility of 99% with 60 FPU/g of glucan enzyme loading, and 92.5% with 10 FPU/g of glucan. The digestibility of ARP treated corn stover was substantially higher than that of alpha-cellulose. The enzymatic digestibility was related with the removal of lignin and hemicellulose, perhaps due to increased surface area and porosity. The SEM pictures indicated that the biomass structure was deformed and its fibers exposed by the pretreatment. The crystallinity index increased with pretreatment reflecting removal of the amorphous portion of biomass. The crystalline structure of the cellulose in the biomass, however, was not changed by the ARP treatment.

575 citations

Journal ArticleDOI
TL;DR: By switching from an acidic medium to a basic one, hydroxide (OH ) exchange membrane fuel cells (HEMFCs) have the potential to solve the problems of catalyst cost and durability while achieving high power and energy density.
Abstract: Hydrogen proton exchange membrane fuel cells (PEMFCs) have been demonstrated to have high power density and reasonable energy density. Their commercialization, however, has been hampered by the high cost and low durability of their electrocatalysts. By switching from an acidic medium to a basic one, hydroxide (OH ) exchange membrane fuel cells (HEMFCs) have the potential to solve the problems of catalyst cost and durability while achieving high power and energy density. In a basic environment, the cathode oxygen reduction over-potential can be significantly reduced, leading to high fuel cell efficiency, and catalysts in basic medium are also more durable. In addition, the facile cathode kinetics allows nonprecious metals to be used as catalysts, thus drastically reducing the cost of the fuel cell. Further, HEMFCs can offer fuel flexibility (e.g., methanol, ethanol, ethylene glycol, etc.) because of their low overpotential for hydrocarbon fuel oxidation and reduced fuel crossover. One of the most significant problems for HEMFCs is the lack of a soluble ionomer that can be used in the catalyst layer to build an efficient three-phase boundary and thus drastically improve the utilization of the catalyst particles and reduce the internal resistance. One of the most desirable properties of an ionomer for use in the catalyst layer is high solubility in low-boiling-point water-soluble solvents such as ethanol and (nor 2-)propanol, because these solvents are easy and safe to handle and remove during the electrode preparation. The ionomer should also have high hydroxide conductivity and alkaline stability. For PEMFCs, Nafion has been the ionomer of choice because it meets these requirements. But for HEMFCs, the most commonly used material for the hydroxide exchange membrane (HEM) is a quaternary ammonium hydroxide containing polymer that has poor solubility in the aforementioned simple solvents, low hydroxide conductivity, and poor alkaline stability. For example, Tokuyama Co. very recently reported two types of soluble quaternary ammonium hydroxide containing polymers (product code: A3Ver2, soluble in tetrahydrofuran or n-propanol, and AS-4, soluble in n-propanol); however, as a result of their low hydroxide conductivity, their incorporation into the catalyst layers of HEMFCs only led to a moderate improvement in performance. In another case, Park et al. prepared an ionomer solution of the trimethylamine (TMA) and N,N,N’,N’-tetramethyl-1,6-hexanediamine (TMHDA) based polysulfone– methylene quaternary ammonium hydroxide (T/TPQAOH) in dimethylacetamide (DMAc, b.p. 166 8C). Similar to the Tokuyama results, the low hydroxide conductivity of the ionomer significantly limited the improvement in fuel cell performance, and in addition, removal of the high-boilingpoint solvent is considered difficult and unsafe in the presence of finely dispersed catalysts. Owing to the lack of a soluble highly conductive solid ionomer, aqueous solutions of KOH or NaOH have been previously used in the electrodes, where the introduction of metal cations (M) offsets the key advantages of a HEMFC over traditional liquid-electrolytebased alkaline fuel cells (AFCs). Furthermore, owing to the lack of a good ionomer as the binder, non-ionic conductive PTFE and proton-conductive Nafion ionomers were used as substitutes in the electrodes, even though these materials were known to have no hydroxide conductivity. Recently, Varcoe et al. reported a TMHDA-based polyvinylbenzylcrosslinked quaternary ammonium hydroxide (TPCQAOH) electrochemical interface to enhance HEMFC performance. Because the polymer used was not soluble in ionomer form, one could question its ability to form an efficient three-phase-boundary structure in the catalyst layer, thereby limiting performance. Moreover, the hydroxide conductivity and stability of the electrochemical interface are still of concern because it is based on quaternary ammonium hydroxide groups. Quaternary phosphonium containing polymers showed excellent solubility in methanol. The strong basicity of the tertiary phosphine suggests that quaternary phosphonium hydroxides are very strong bases. Therefore in this work, we synthesized a new quaternary phosphonium based ionomer that is soluble in low-boiling-point water-soluble solvents and is highly hydroxide conductive: tris(2,4,6-trimethoxyphenyl) polysulfone-methylene quaternary phosphonium hydroxide (TPQPOH; Scheme 1). The TPQPOH ionomer exhibits excellent solubility in pure methanol, ethanol, and n-propanol and in their aqueous solutions (50 wt% in water, see Table S1 in the Supporting Information). On the other hand, the TPQPOH is insoluble in pure water, even at 80 8C, suggesting that it can be used in the [*] Dr. S. Gu, Dr. R. Cai, T. Luo, Dr. Z. Chen, M. Sun, Y. Liu, Prof. Dr. Y. S. Yan Department of Chemical and Environmental Engineering University of California—Riverside Riverside, CA 92521 (USA) Fax: (+1)951-827-5696 E-mail: yushan.yan@ucr.edu Homepage: http://www.engr.ucr.edu/faculty/chemenv/ yushanyan.html

551 citations

Journal ArticleDOI
04 Aug 2004-Langmuir
TL;DR: A fundamental knowledge of the synthesis and optical properties of Ru(bpy) dye-doped silica nanoparticles is provided, which can be easily manipulated, with regard to particle size and size distribution, and bioconjugated as needed for bioanalysis and bioseparation applications.
Abstract: Fluorescent labeling based on silica nanoparticles facilitates unique applications in bioanalysis and bioseparation. Dye-doped silica nanoparticles have significant advantages over single-dye labeling in signal amplification, photostability and surface modification for various biological applications. We have studied the formation of tris(2,2'-bipyridyl)dichlororuthenium(II) (Ru(bpy)) dye-doped silica nanoparticles by ammonia-catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) in water-in-oil microemulsion. The fluorescence spectra, particle size, and size distribution of Ru(bpy) dye-doped silica nanoparticles were examined as a function of reactant concentrations (TEOS and ammonium hydroxide), nature of surfactant molecules, and molar ratios of water to surfactant (R) and cosurfactant to surfactant (p). The particle size and fluorescence spectra were dependent upon the type of microemulsion system chosen. The particle size was found to decrease with an increase in concentration of ammonium hydroxide and increase in water to surfactant molar ratio (R) and cosurfactant to surfactant molar ratio (p). This optimization study of the preparation of dye-doped silica nanoparticles provides a fundamental knowledge of the synthesis and optical properties of Ru(bpy) dye-doped silica nanoparticles. With this information, these nanoparticles can be easily manipulated, with regard to particle size and size distribution, and bioconjugated as needed for bioanalysis and bioseparation applications.

461 citations

Journal ArticleDOI
TL;DR: The effect of ammonia concentration on the region of existence of single-phase water-in-oil microemulsions has been investigated for the system polyoxyethylene (5) nonylphenyl ether (NP-5)/cyclohexane/ammonium hydroxide and shows a complex dependence of the particle size on the water-to-surfactant molar ratio (R) and on the concentration of ammonium Hydroxide.
Abstract: The effect of ammonia concentration on the region of existence of single-phase water-in-oil microemulsions has been investigated for the system polyoxyethylene (5) nonylphenyl ether (NP-5)/cyclohexane/ammonium hydroxide. The presence of ammonia decreases the size of the microemulsion region. A minimum concentration of surfactant (estimated at about 1.1 wt%) is required for solubilization of the aqueous phase; this value is not significantly affected by ammonia concentration. As indicated by fluorescence spectral data, the transition between bound and free water occurs when the water-to-surfactant molar ratio is about 1 and the presence of ammonium hydroxide does not appear to have a significant effect on this. Ultrafine (30-70 nm diameter), monodisperse silica particles produced by hydrolysis of tetraethoxysilane (TEOS) in the microemulsion show a complex dependence of the particle size on the water-to-surfactant molar ratio (R) and on the concentration of ammonium hydroxide. At relatively low ammonia concentration in the aqueous pseudophase (1.6 wt% NH3) the particle size decreases monotonically with increase in R. However, for higher ammonia concentrations (6.3-29.6 wt% NH3) a minimum in particle size occurs as R is increased. These trends are rationalized in terms of (a) the effects of the concentration, structure, and dynamics of the NP-5 reverse micelles on the hydrolysis and condensation reactions of TEOS, and (b) the effects of ammonia concentration on the stability of the microemulsion phase, the hydrolysis/condensation reactions of TEOS, and the depolymerization of siloxane bonds. Copyright 1999 Academic Press.

386 citations

Journal ArticleDOI
TL;DR: The X-ray crystallography data indicate that the basic crystalline structure of the cellulosic component of corn stover is not altered by the ARP treatment, and low-liquid ARP can reduce the liquid throughput and residence time to 3.3 mL/g-biomass and 10-12 min, without adversely affecting the overall effectiveness.
Abstract: Corn stover was pretreated with aqueous ammonia in a flow-through column reactor, a process termed as Ammonia Recycle Percolation (ARP). The aqueous ammonia causes swelling and efficient delignification of biomass at high temperatures. The ARP process solubilizes about half of xylan, but retains more than 92% of the cellulose content. Enzymatic digestibility of ARP-treated corn stover is 93% with 10 FPU/g-glucan enzyme loading. The SEM pictures and FTIR spectra confirm swelling and delignification effects of the ARP process. The X-ray crystallography data indicate that the basic crystalline structure of the cellulosic component of corn stover is not altered by the ARP treatment. Low-liquid ARP can reduce the liquid throughput and residence time to 3.3 mL/g-biomass and 10-12 min, without adversely affecting the overall effectiveness. The low-water ARP achieved 73.4% delignification and 88.5% digestibility with 15 FPU/g-glucan. The ethanol yield from the SSF of low-liquid ARP-treated corn stover using Saccharomyces cerevisiae reached 84% of the theoretical maximum. Successive operation of a hot-water treatment and the ARP was applied as a method of biomass fractionation. The two-stage process separated xylan in the first stage (84%) and lignin in the second stage (75%), resulting treated solid that contains 79% glucan.

361 citations

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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202143
202090
2019186
2018217
2017235
2016201