Chapters 1-4 Flashcards
Why banana?
- (BG) Banana wastes are also part of the growing concern of agricultural community and improper treatment may lead to excessive GHG and may even contaminate water. As a way to promote sustainable solutions, we opt to use banana peel wastes and turn them to something usable.
-Also, according to a study, out if 6 lignocellulosic materials including water hyacinth, coffee grounds, banana peels, and coconut shells, banana peels had the highest adsorption capacity for nickel ions and also high adsorption capacity for lead ions based on the results shown by Langmuir isotherm. - (BG) We chose banana as our raw material because, of course, it’s cheap, it’s accessible, and you can obtain it basically anytime and anywhere. It has been scientifically proven that banana peels contain variety of functional groups such as amide, hydroxyl, and carboxyl, groups which can chemically bind with heavy metal ions which makes it potential raw material for biochar. explain the functional groups
- (2.4.4) Studies also show that agricultural wastes such as banana peels have notably high adsorption capacity for contaminants such as manganese II, cadmium, and lead.
- Why saba in particular?
This banana specie is chosen because of its availability and abundance.
other reasons
Why pickering emulsion? explain the mechanism/ science behind
The creation of spherical adsorbents have been expensive and complicated. The emulsion template method is a good way of producing porous materials with high adsorption effectiveness. However, it uses surfactants that are often made through chemical processes. (Surfactants act as stabilizers or emulsifying agent to keep the oil as droplets in water. They have hydrophilic part directed towards the water and hydrophobic one towards the oil.). A good alternative is to use the Pickering emulsion method which uses solid particles located at the interface of oil and water instead of surfactants to stabilize the emulsion and prevent coalescence of particles. It creates spherical objects with uniform morphology. It can also dissolve functional monomers with varying polarity since it is compatible with a variety of functional nanomaterials. The particle has to have a high contact angle to the interface to prevent coalescence of droplets.
-Pickering emulsion has low manufacturing sots and fewer undesirable effects.
Explain the adsorption mechanism
During adsorption which is a heat-releasing process, contaminants or adsorbate are extracted and bind to a solid surface which is the adsorbent due to weak physical forces like van der Waals (physisorption) or covalent forces (chemisorption).
The surface of biochar has functional groups including hydroxyl, carbonyl, and carboxyl groups that allows for various interaction between molecules such as nutrients and pollutants.
-In the case of adsorption of zinc onto the biochar, strong chemical adsorption occurs, particularly electrostatic interactions. The positively charged heavy metal ions are attracted to the negatively charged hydroxyl and carboxyl groups on the biochar surface. This attraction is strong enough to hold the heavy metal ions onto the surface.
Hydroxyl (-OH) groups are formed during the dehydration of cellulose and hemicellulose during pyrolysis. They can form hydrogen bonds with water molecules, making biochar more hydrophilic, making it more easily wetted by water Carboxyl (-COOH) groups are formed from the oxidation of carbonyl and methylene groups during pyrolysis. They can deprotonate or release hydrogen ions (H+) giving the biochar a net negative charge which allows the biochar to attract and adsorb positively charged pollutants.
- What stabilizer will you use in pickering emulsion?
We will use a synergistic combination of semi-coke and sodium alginate. SC is a byproduct of distillation shale oil which contains 80% inorganic minerals like kaolinite, quartz, hematite, and carbonate with organic components like aliphatic compounds. It possesses diverse porous structures similar to biochar. It is a porous material with a large surface area. It is insoluble in water. SA prevents coalescence and maintains stability during storage. It is a naturally occurring anionic or negatively charged polysaccharide featuring numerous carboxyl and hydroxyl groups in its molecular structure and has the capacity to bind with most divalent or multivalent metal ions (positively charged). It forms a viscous gel that acts as a barrier between oil droplets.
When SA and SC are mixed, they create very stable pickering emulsion. SC provides strong adsorption site for oil droplets, while SA helps to prevent droplets from coalescing.
How to obtain adsorption rate (x and y)
We are going to use batch adsorption experiment where the adsorbent is mixed with adsorbate in a container and is then agitated for a specified time. The concentration of adsorbate in the solution is measured at intervals. The adsorption rate can be calculated from the change in adsorbate concentration over time.
What isotherms to be used?
First, adsorption isotherms help in predicting the behavior of adsorption systems.
For this study, we are going to employ three adsorption isotherms: langmuir, freundlich, and redlich-peterson.
Langmuir isotherm assumes a monolayer adsorption. If our data points best fit this isotherm, it indicates that there are no interactions between the molecules of the adsorbate, only between the adsorbate and adsorbent. The heat of adsorption and the affinity of adsorbates are also equal for all adsorption sites.
If our data points best fit the freundlich isotherm, this means that there is heterogeneity in the adsorbent. This indicates that the adsorbates have different affinities to the adsorption sites.
Redlich peterson isotherm, on the other hand, has the features of both langmuir and freundlich isotherms. It presents a sigmoidal curve where it approaches langmuir isotherm at high concentration and freundlich isotherm at low concentrations.
Chemical and analytical methods to be used
-After size reduction, chemical activation is done. The banana peel will be mixed and soaked with potassium acetate (1:1 ratio) and distilled water. This will be heated gradually from 27C to 700C, at a rate of 10C/min under inert atmosphere of N2. Inert atmosphere will prevent oxidation, allows better control of reaction conditions, safety (reduces risk of fire or explosion), and prevents moisture uptake. KAc decomposes during pyrolysis, releasing K+ ions and acetate ions that interact to biomass components. These serve as catalysts for the dehydration and dealkylation of cellulose and hemicellulose of biomass to remove water and alkyl groups. As water and alkyl groups are removed, more carbon atoms are exposed which converts the biomass to a carbon-rich material. K+ ions also leads to the formation of a porous structure within biochar due to the disruption of the biomass matrix by the ions, creating pores and enhancing surface area of the biochar.
-Acid treatment was conducted by a cleaning procedure using 0.1 M HCl to attain a neutral pH for the resultant biochar.
-Untreated biochar will be submerged in NaOH. This alkali treatment modifies the physicochemical characteristics of biochar. It introduces porosity, increases surface area, increases hydroxyl and carboxyl groups, and biochar’s hydrophilicity, and improved thermal stability.
-The treated biochar will be mixed with sodium alginate then added to deionized water to generate a mixed aqueous solution. Pickering emulsion increases the surface area, creates a spherical morphology, and produced porous material with high adsorption capacity. Corn oil is the dispersion phase and water is the dispersion medium.
For the analytical or characterization methods, the structural examination of SB will be conducted using FTIR, surface characteristics using SEM, zeta potential using a Zetasizer, and Thermogravimetric analysis. Zeta potential is a measure of the electrostatic repulsion or attraction between particles, and it plays a crucial role in determining the stability of colloidal dispersions. When particles have a high zeta potential, either positive or negative, they repel each other, preventing aggregation and sedimentation. This results in stable and well-dispersed suspensions. Conversely, when particles have a low zeta potential, they tend to agglomerate and settle out of the suspension. This can lead to flocculation, which is the formation of larger flocs or aggregates of particles.
For the analytical or characterization methods, the structural examination of SB will be conducted using FTIR, surface characteristics using SEM, zeta potential using a Zetasizer, and Thermogravimetric analysis. Zeta potential is a measure of the electrostatic repulsion or attraction between particles, and it plays a crucial role in determining the stability of colloidal dispersions. When particles have a high zeta potential, either positive or negative, they repel each other, preventing aggregation and sedimentation. This results in stable and well-dispersed suspensions. Conversely, when particles have a low zeta potential, they tend to agglomerate and settle out of the suspension. This can lead to flocculation, which is the formation of larger flocs or aggregates of particles.
Is it precipitation or aqueous solution
The solution of biochar, sodium alginate, then added to water, will be aqueous solution. The mixture of biochar and sodium alginate is dispersed in the water which is the medium.
The adsorption of heavy metals in wastewater forms an aqueous solution as it just involves the attachment of the ions to the surface of the biochar. Precipitation occurs when a solid phase is formed due to solubility limit.
Why did you choose zinc
Zinc is among the major pollutants or heavy metals of wastewater and are known to be hazardous if left untreated. As the researchers cannot generalize the entire mechanism of different heavy metals in wastewater, only Zn2+ are considered.
- What is the advantage of adsorption among other methods of wastewater treatment (e.g. RO, coagulation, flocculation)
Adsorption is known for its versatility, high efficacy, low energy requirement, and cost-effectiveness.
Explain biochar, how’s its made
Biochar is a carbon-rich, charcoal-like substance produced by pyrolysis of organic material from biomass. Pyrolysis is a thermochemical process that involves heating biomass in the absence of oxygen. It has a high carbon content, and porous structure. Biochar has high specific surface area, total pore volume, and abundance of surface functional groups such as hydroxyl and carboxyl groups. Higher SBET will provide larger surface area for interaction and provides more sites for contaminants to bind to, enhancing the adsorption capacity. It also exhibits combination of micro, macro- and mesophores. Micropores provide higher SSA. The pore volume is the total volume of pores within the material.
- What factors to consider when creating biochar?
Pyrolysis temperature must be optimal because at high temperatures more surface area and carbon content are achieved. However, as the temperature arises, yields of biochar declines. The type of biomass also affects the efficiency and effectivity of biochar. The rate of adsorption depends, not only on the type of the adsorbate, but also on the type of the adsorbent material.
- Source of saba banana? Will you buy it?
The bananas will be resourced from vendors around Metro Manila.
- Why spherical biochar? Explain the science/rationale behind this
Because clean biochar has some drawbacks, such as weak adsorption capacity, a limited adsorption range, and other deficiencies, biochar must be modified to broaden its practical application in the removal of pollutants from water.
The messy morphology of non-spherical biochar influences its separation efficiency and repeatability of the results. Studies have shown that Spherical biochars haveimproved adsorption capacity, mechanical strength, regularly shaped surface, and high micropore volume.
- How will you make biochar?
So after the ground biomass is chemically activated by potassium acetate, the mixture will be heated in a pyrolytic reactor at temperatures from 27C to 700C, at a rate of 10C/min under N2 inert atmosphere to prevent moisture uptake from the air and also prevent fires and explosions.
- What are the objectives of your study?
Generally, we want to determine the effectiveness kf saba banana as a raw material for biochar for the adsorption of zinc in a simulated wastewater.
Specifically, we want to compare the morphology and adsorption capacity of the banana-peel based biochar with and without pretreatment and how do our biochar compare with other banana-peel based biochars on literature. We will also determine the suitable isotherm for the adsorption mechanism.
- What is the significance of NaOH pretreatment in your study (being included on the specific objectives)? Why the need to compare?
Untreated biochar will be submerged in NaOH. This alkali treatment modifies the physicochemical characteristics of biochar. It introduces porosity, increases surface area, increases hydroxyl and carboxyl groups, and biochar’s hydrophilicity, and improved thermal stability. We wanted to compare because it will help us evaluate the necessity of alkali treatment in synthesizing spherical biochars.
