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Development of Sustainable Biobased Polymer and Bio-Nanocomposite Materials Using Nanocellulose Obtained from Agricultural Biomass
Published in Linda Godfrey, Johann F Görgens, Henry Roman, Opportunities for Biomass and Organic Waste Valorisation, 2020
A Mtibe, S Muniyasamy, TE Motaung
The main aim of treating cellulosic fibres with alkali is to solubilise hemicellulose, lignin and extractives (Rosa et al., 2010). Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are commonly used alkalis. The treatment with alkali at higher temperatures of about 75ºC to 80ºC is used for solubilisation process (Motaung & Mtibe, 2015). A treatment with strong alkali could affect the crystallinity of the cellulose and degradation could occur (Ridzuan et al., 2015). Following alkaline treatment, the material undergoes several repetitions of washes with water until a neutral pH level is achieved. This treatment swells the fibres and leaves some traces of alkali. These remaining traces of alkali make the fibres more accessible to other chemical treatments and mechanical processes.
Basic Chemical Principles
Published in John A. Conkling, Christopher J. Mocella, Chemistry of Pyrotechnics, 2019
John A. Conkling, Christopher J. Mocella
Most of the common bases are ionic compounds consisting of a positive metal ion and the negatively charged hydroxide ion, OH−. Examples include sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide, Ca(OH)2. Ammonia (NH3) is a weak base, capable of reacting with H+ to form the ammonium ion, NH4+.
Hydrolysis
Published in Richard A. Larson, Eric J. Weber, Reaction Mechanisms in Environmental Organic Chemistry, 2018
Richard A. Larson, Eric J. Weber
In addition to nucleophilic attack by H2O (neutral hydrolysis), we find that hydrolytic reactions are sensitive to specific acid and specific base catalysis (i.e., catalysis by hydronium ion, H+, and hydroxide ion, OH−, respectively). Accordingly, hydrolysis kinetics must take into account the potential for H2O to dissociate. Even at pH 7.0, where the concentration of H+ and OH− is only 10−7 M, specific acid and specific base catalysis can significantly accelerate hydrolysis kinetics. Specific acid and base catalysis occurs because the hydronium ion and hydroxide ions provide an alternative mechanism for hydrolysis that is energetically more favorable. In specific acid catalysis, hydronium ion is thought to provide a reaction pathway of lower energy by withdrawing electron density from the atom bearing the leaving group, X, thus making it more susceptible to nucleophilic attack by H2O. Specific base catalysis occurs because OH− is a much more reactive nucleophile than H2O (typically by a factor of about 104: Streitwieser, 1962). Accordingly, a hydrolysis reaction involving nucleophilic attack by OH” will occur at a faster rate than the pathway involving nucleophilic attack by H2O alone.
Activated carbon based paste electrodes for the simultaneous and effective detection of divalent cadmium and lead ions in wastewater
Published in Environmental Technology, 2023
S. P. Aravind, T. P. Anandhu, Karthik Jayakumar, Ashna Appukuttan, B. Rahul Krishna, J. Amala, S. Bhuvaneshwari
The pH significantly affects the voltammetric detection of cadmium and lead. The pH of the heavy metal solutions was varied between 2 and 4.5 using H2SO4. Electrochemical responses respective to Cd2+ and Pb2+ were recorded for all 3 electrodes using CV, as shown in Figure 3. The optimum pH for the detection of both Cd2+ and Pb2+ using all three electrodes was found to be 3, where the current intensity was maximum. The trend of reduction peak current with pH is given in the inset images of Figure 3. Below pH 3, a lower peak current was obtained, possibly due to the competition of H+ ions with the heavy metal ions for the electrode surface. Whereas at high pH, there is a considerable decrease in the current density. This perspective may be supported by the introduction of metals into the hydrolysis process. In fact, during the hydrolysis of water, hydroxide ions are produced. These hydroxide ions may then interact with cadmium and lead ions, causing hydrolysis of heavy metal ions to form Cd(OH)+ and Pb(OH)+. The reduction in accessible charges is followed by a fall in current density at the electrode surfaces under these circumstances [26,27]. Therefore, all electrochemical measurements were carried out at a pH of 3 throughout the study.
Microstructure and chemo-physical characterizations, thermal properties, and modeling of the compression stress-strain behavior of lime-based roof and screed paste
Published in European Journal of Environmental and Civil Engineering, 2022
Chiya Y. Rahimzadeh, Ahmed Salih Mohammed, Azeez A. Barzinjy
Figure 12 depicts scanning electron microscopy pictures of the micromorphological properties of hydrated LRP (after 28 days of cure) following specimen failure. Microscopically, Figure 12a depicts an uncompacted microstructure of the hydrated material with many big and small holes. At this size, existing masses are divided into two broad categories: agglomerated grains and unevenly structured surface sheets. After hydration, Portlandite forms cleavage flakes, which are flexible sheets (Ashraf & Olek, 2016). The hydrated LRP sample exhibited XRD peaks at 2θ = 23°, 29.4°, 34°, 35.9°, 39°, 43°, 47.5°, 48.5°, 57.4°, 60.6°, and 64.8°. The majority of peaks in Figure 13 are composed of Portlandite (Ca(OH)2), coesite (SiO2), and calcite (CaCO3), confirming that the general composition of the material consists of these two compounds. Figure 12b and the EDX diagram for the upper point demonstrate that the calcium and silica content of Portlandite sheets was more than 28 and 42 percent, respectively. In this part, about 10% of the aluminum was also observed, which can be involved in forming these sheets. Furthermore, the rod forms in Figure 12b indicate aragonite (Espitia Morales & Castellanos, 2021). They are generally unstable and convert into portlandite sheets as the hydration progresses. Figure 12a illustrates two distinct textures: an agglomerated texture that is spongy and porous, known as disordered calcite (Longo et al., 2020), and a flaky texture that is solid and crystalline without any pores. As previously mentioned, this is calcium-silicate. The agglomerated textures are created from the combination of the growing fluffy crystals during the hydration process, as shown in Figure 12. In addition, the temperature and carbonation as the curing conditions severely affect completing the reactions of calcium-silicate (C-S) bonding and calcination (Safari et al., 2020; Yang et al., 2017). According to the EDX analysis results in Figure 12b, silica and calcium are the most abundant components in both textures. Hydroxide is a diatomic anion with the chemical formula OH −. It consists of an oxygen and hydrogen atom held together by a single covalent bond and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. Disiloxane groups, Si–O–Si, tend to have larger bond angles than their carbon counterparts, C–O–C. The Si–O–Si angle ranges from about 130–180°, whereas the C–O–C angle in ethers is typically 107–113°. Si–O–C groups are intermediate, tending to have bond angles smaller than Si–O–Si but larger than C–O–C.