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Adsorbents
Published in Deepak Gusain, Faizal Bux, Batch Adsorption Process of Metals and Anions for Remediation of Contaminated Water, 2021
Shikha Dubey, Deepak Gusain, Yogesh Chandra Sharma, Faizal Bux
The interaction between the adsorbate and the adsorbent is largely affected by the surface chemistry of the adsorbent, especially for the case where adsorption of ions occurs onto oxidic surfaces (Worch 2012a). In this perspective, the pHpzc of the adsorbent assists in the comprehension of the influence of pH on the overall adsorption of charged species on their surfaces. The point of zero charge (pHpzc) evaluates the point at which any adsorbent is electrically neutral in nature and is referred to as a region in the pH scale where the surface bears a net zero charge due to the equal sum of positive and negative charges on the surface of the adsorbent. When the pH of the medium is lower than the pHpzc of the adsorbent – the surface becomes positively charged and the medium becomes acidic due to donation of protons more than the hydroxide groups by the acidic water (Roushani et al. 2017). Thus, attraction of negatively charged species becomes feasible toward positive adsorbent surface. On the contrary, at a pH value higher than the pHpzc, the surface bears negative charges elicited by the attraction of cations and vice versa. The point of zero charge (pHpzc) is the characteristic feature of adsorbents. Generally, the electrostatic attraction/repulsion forces strongly affect the adsorption of charged adsorbate molecules on the charged adsorbent surfaces (Worch 2012a; Hua et al. 2012; Ali 2012).
Waste Hemp (Cannabis sativa) Fibers as a Biosorbent and a Precursor for Biocarbon Sorbents: Influence of their Chemical Composition on Pb(II) Removal
Published in Tatjana Stevanovic, Chemistry of Lignocellulosics: Current Trends, 2018
Mirjana Kostic, Biljana Pejic, Marija Vukcevic
Additionally, the acid-base behavior of biosorbent and biocarbon samples was examined through the point of zero charge (PZC) determination. The PZC of the tested biosorbents and biocarbons was determined by mass titration (Vukčević et al., 2008). Point of zero charge pH (pHPZC) is a pH of the solution at which the overall observed charge on the sorbent surface is zero. At the solution pH less then pHPZC, functional groups are protonated, sorbent behaves as positively charged and repel the positive metal ions. On the other hand, increase in pH above pHPZC makes the functional groups deprotonated, they act as negative species and attract and bind positive metal ions.
Metal–Polymer Composite Biomaterials
Published in Severian Dumitriu, Valentin Popa, Polymeric Biomaterials, 2020
Active surface hydroxyl groups dissociate in aqueous solutions and form electric charges, as shown in Figure 12.10b.16–19 Positive or negative charge due to the dissociation is governed by the pH of the surrounding aqueous solution: Positive and negative charges are balanced and apparent charge is zero at a certain pH. This pH is the point of zero charge (pzc). The pzc is the unique value for an oxide and an indicator that the oxide shows acidic or basic property. For example, in the case of TiO2, the pzc of rutile is 5.3 and that of anatase is 6.2.16 In other words, anatase surface is acidic at smaller pH and basic at larger pH than 6.2. Active surface hydroxyl groups and electric charges formed by the dissociation of the groups play important roles for the bonding with polymers and immobilization of molecules. Therefore, the concentration of surface hydroxyl group and pH are important factors for the bonding with polymeric materials and immobilization of molecules.
Malachite green (cationic dye) removal with modified Pinus brutia biochar
Published in International Journal of Phytoremediation, 2023
Okan Bayram, Uğur Özkan, Halil Turgut Şahin, Fethiye Göde
The pH level at which a solid material has no net charge and an equal amount of positive and negative charges on its surface is known as the Point of Zero Charge (PZC). A solid material’s PZC can be found using the mass titration method by titrating its surface with a mild acid or basic solution. The solid item is weighed and suspended in a solution with a known pH in this approach. After adding a weak acid or base to the solution to vary the pH, the solid material’s mass is changed and measured. This procedure is repeated until the solid material’s PZC is reached, which is indicated by the minimum mass change. The PZC determines the net charge on the surface of the material and can have an impact on its solubility, adsorption, and reactivity, making it an important feature for understanding the behavior of solid materials in solution. The mass titration method is a straightforward and easy way to figure out a material’s PZC, but it can take some time and requires precise measurement of the solid material’s mass change (Reymond and Kolenda 1999; Bourikas et al. 2003; Rubangakene et al. 2023; Yun and Chandler 2023; Zein et al. 2023). While measuring the points of zero charges of PBB (Figure 2) and nM-PBB (Figure 3), various amounts of PBB and nM-PBB were added to 40 mL of solution and the pH values were measured after shaking for 24 h.
Insight into the adsorptive mechanisms of methyl violet and reactive orange from water—a short review
Published in Particulate Science and Technology, 2023
Azrul Nurfaiz Mohd Faizal, Nicky Rahmana Putra, Muhammad Abbas Ahmad Zaini
The adsorption mechanisms of dye removal are regulated by the operating conditions (e.g., temperature, contact time, concentration, etc.) and physical attributes of adsorbent (e.g., pH of the point of zero charge, particle size, etc.). Often, the capacity decreases with temperature, in which heat is released and the adsorption is exothermic (Mohammadi et al. 2010). At this point, the adsorbate-adsorbent interaction is weak, so the existing attraction forces are easily breaking off as solution temperature increases (Abbas et al. 2012; Li et al. 2013). Meanwhile, the adsorption is endothermic when heat is absorbed, wherein the capacity rises with solution temperature because of the increased mobility of molecules (Abbas et al. 2012). The pH of the point of zero charge (pHPZC) is defined as the pH at which the adsorbent surface has a net neutral charge. If the solution pH>pHPZC, the adsorbent is anionic with negatively charged surface to attract cationic dye, while for solution pH<pHPZC, the adsorbent is cationic that is favorable toward anionic dye (Zanella, Tessaro, and Féris 2015).
Eco-friendly synthesis of a novel adsorbent from sugarcane and high-pressure boiler water
Published in Environmental Technology, 2023
Alexandre Amado de Moura, Henrique Straioto, Wardleison Moreira Martins, Thiago Peixoto de Araújo, Alexandre Diório, Guilherme Andreoli Gil, Murilo Pereira Moisés, Maria Angélica Simões Dornellas Barros
The pH of the point of zero charge (pHPZC) is an important parameter for the adsorption process. When the contaminated solution presents pH < pHPZC the adsorbent remains in its protonated form with a positive net charge in its surface which favours the adsorption of anionic contaminants. In contrast, for solutions with pH > pHPZC, the adsorbent is deprotonated with a negative superficial net charge and, hence, the adsorption of cationic contaminants is favoured [35]. The pHPZC of HC and HC-T adsorbents are shown in The results shown in Figure 5 revealed that the adsorbents presented acids values for pHPZC for both materials being 4.02 and 3.46 for HC and HC-T, respectively. The acid pHPZC for the adsorbents was due to the presence of acid groups in the material after their synthesis. Therefore, performing the adsorption at pH > pHPZC implies that the adsorbent surface will be negatively charged and, hence, enhance the adsorption of cationic molecules such as DIU and MB [36].