skip to main content

Title: Student explorations of calcium alginate bead formation by varying pH and concentration of acidic beverage juices
Abstract Teaching experiments involving edible, biodegradable calcium alginate beads serve as an attractive model system to introduce upper secondary age students to core chemistry topics through innovations in sustainable consumer products. A teaching experiment is described that engages students with the synthesis of calcium alginate hydrogel beads from sodium alginate and calcium lactate, two food-safe and renewable materials. The beads’ outer membranes are a result of ionic interactions between carboxylate groups from alginate strands and the divalent calcium cations between them, thus forming cross-linked polymers. Protonation of the carboxylate groups on the alginate strands decreases crosslinking density affecting bead formation. First, various concentrations of citric acid are used to lower the pH of the sodium alginate solution and the effect on the calcium alginate bead formation is observed. A correlation between pH and bead shape and firmness is derived. This information is then used to explore juices with varying natural acidities. The experiment is amenable to implementation in the classroom or as an at-home activity. Learning outcomes include acid-base reactions, chemical bonding, polymer structures, and green chemistry concepts. Students consider the environmental challenges of traditional plastics used in packaging and how innovative new commercial products are attempting to provide solutions.
; ; ; ;
Award ID(s):
1559833 2011401 1901635
Publication Date:
Journal Name:
Chemistry Teacher International
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Hydrogel-encapsulated catalysts are an attractive tool for low-cost intensification of (bio)-processes. Polyvinyl alcohol-sodium alginate hydrogels crosslinked with boric acid and post-cured with sulfate (PVA-SA-BS) have been applied in bioproduction and water treatment processes, but the low pH required for crosslinking may negatively affect biocatalyst functionality. Here, we investigate how crosslinking pH (3, 4, and 5) and time (1, 2, and 8 h) affect the physicochemical, elastic, and process properties of PVA-SA-BS beads. Overall, bead properties were most affected by crosslinking pH. Beads produced at pH 3 and 4 were smaller and contained larger internal cavities, while optical coherence tomography suggested polymer cross-linking density was higher. Optical coherence elastography revealed PVA-SA-BS beads produced at pH 3 and 4 were stiffer than pH 5 beads. Dextran Blue release showed that pH 3-produced beads enabled higher diffusion rates and were more porous. Last, over a 28-day incubation, pH 3 and 4 beads lost more microspheres (as cell proxies) than beads produced at pH 5, while the latter released more polymer material. Overall, this study provides a path forward to tailor PVA-SA-BS hydrogel bead properties towards a broad range of applications, such as chemical, enzymatic, and microbially catalyzed (bio)-processes.

  2. A novel composite hydrogel bead composed of sodium alginate (SA) and aldehyde cellulose nanocrystal (DCNC) was developed for antibiotic remediation through a one-step cross-linking process in a calcium chloride bath. Structural and physical properties of the hydrogel bead, with varying composition ratios, were analyzed using techniques such as BET analysis, SEM imaging, tensile testing, and rheology measurement. The optimal composition ratio was found to be 40% (SA) and 60% (DCNC) by weight. The performance of the SA–DCNC hydrogel bead for antibiotic remediation was evaluated using doxycycline (DOXY) and three other tetracyclines in both single- and multidrug systems, yielding a maximum adsorption capacity of 421.5 mg g−1 at pH 7 and 649.9 mg g−1 at pH 11 for DOXY. The adsorption mechanisms were investigated through adsorption studies focusing on the effects of contact time, pH, concentration, and competitive contaminants, along with X-ray photoelectron spectroscopy analysis of samples. The adsorption of DOXY was confirmed to be the synergetic effects of chemical reaction, electrostatic interaction, hydrogen bonding, and pore diffusion/surface deposition. The SA–DCNC composite hydrogel demonstrated high reusability, with more than 80% of its adsorption efficiency remaining after five cycles of the adsorption–desorption test. The SA–DCNC composite hydrogel bead could be a promisingmore »biomaterial for future antibiotic remediation applications in both pilot and industrial scales because of its high adsorption efficiency and ease of recycling.« less
  3. Abstract

    The recovery and reuse of phosphorus (P) from wastewater treatment process is a critical and viable target for sustainable P utilization. This study explores a novel approach of integrating ultrafine mineral particles into hydrogel matrixes for enhancing the capacity of phosphate adsorption. Dolomite‐alginate (DA) hydrogel beads were prepared by integrating ball‐milled, ultrafine dolomite powders into calcium cross‐linked alginate hydrogel matrix. The adsorption isotherms followed a Langmuir–Freundlich adsorption model with higher specific adsorption capacity than those reported in literature. The kinetics of phosphate adsorption suggest that the adsorption is diffusion controlled. Investigation of adsorption capacity at differentpHshowed a maximum adsorption capacity in thepHrange of 7–10. Lastly, we demonstrated that theDAbeads are capable of slowly releasing most of the adsorbed phosphate, which is an important criterion for them to be an effective phosphorous fertilizer. This study, usingDAcomposite hydrogel as an example, demonstrates a promising strategy of immobilizing ultrafine mineral adsorbents into biocompatible hydrogel matrix for effective recovery of phosphorous resource from wastewater.

    Practitioner points

    Integration of dolomite and alginate hydrogel beads is demonstrated using ball milling.

    Ball milling process increases the specific adsorption capacity of dolomite on phosphorus.

    Adsorption isotherms, kinetics, andpHeffects of the dolomite–alginate beads are investigated.

    Themore »dolomite–alginate beads can be used as slow‐release phosphorus fertilizer.

    « less
  4. Despite national and international regulations, plastic microbeads are still widely used in personal care and consumer products (PCCPs) as exfoliants and rheological modifiers, causing significant microplastic pollution following use. As a sustainable alternative, microbeads were produced by extrusion of biomass solutions and precipitation into anti-solvent. Despite using novel blends of biodegradable, non-derivatized biomass including cellulose and Kraft lignin, resulting microbeads are within the shape, size, and stiffness range of commercial plastic microbeads, even without crosslinking. Solution processability and resulting bead shape and Young’s modulus can be tuned via biomass source, concentration, and degree of polymerization; biomass concentration, extrusion geometry, and precipitation and extraction conditions control the bead size. Lignin incorporation reduces the solution viscosity, which improves processability but also produces flatter beads with higher moduli than cellulose-only microbeads. While some lignin leaches from the beads when stored in water, adding surfactants like sodium dodecyl sulfate suppresses this effect, resulting in good mechanical stability over 2 months with no noticeable structural degradation. The stability of these mixed-source biomass microbeads—despite the absence of chemical crosslinking or derivatization—makes this route a promising, robust approach for obtaining environmentally-benign microbeads of tunable size and stiffness for use in PCCPs.
  5. Obtaining insights into the adsorption and assembly of polyelectrolytes on chemically variable calcium silicate hydrate (C-S-H) surfaces at the atomic scale has been a longstanding challenge in the chemistry of sustainable building materials and mineral–polymer interactions. Specifically, polycarboxylate ethers (PCEs) based on acrylate and poly(ethylene glycol) acrylate co-monomers are widely used to engineer the fluidity and hydration of cement and play an important role in the search for building materials with a lower carbon footprint. We report the first systematic study of PCE interactions with C-S-H surfaces at the molecular level using simulations at single molecule coverage and comparisons to experimental data. The mechanism of adsorption of the ionic polymers is a two-step process with initial cation adsorption that reverses the mineral surface charge, followed by adsorption of the polymer backbone through ion pairing. Free energies of binding are tunable in a wide range of 0 to −5 kcal mol −1 acrylate monomer. Polymer attraction increases for higher calcium-to-silicate ratio of the mineral and higher pH value in solution, and varies significantly with PCE composition. Thereby, successive negatively charged carboxylate groups along the backbone induce conformation strain and local detachment from the surface. Polyethylene glycol (PEG) side chains in themore »copolymers avoid contact with the C-S-H surfaces. The results guide in the rational design of adsorption strength and conformations of the comb copolymers, and lay the groundwork to explore the vast phase space of C-S-H compositions, surface morphologies, electrolyte conditions, and PCE films of variable surface coverage. Chemically similar minerals and copolymers also find applications in other structural and biomimetic materials.« less