Geopolymer beads and 3d printed lattices containing activated carbon and hydrotalcite for anionic dye removal

Screening of different lamellar solids for the adsorption of phenolic compounds from grape pomace

Grape pomace (GP) is recognized as a valuable source of polyphenols, prompting research into new therapeutic molecules while enhancing this by-product value. To address low stability and bioavailability issues of phenolic compounds, lamellar solids emerge as a promising approach for their loading and stabilization in food, cosmetic, and pharmaceutical applications. A solid phase adsorption procedure was developed here by comparing the properties of eight solids towards GP polyphenols. Magnesium aluminium azelate showed nearly complete adsorption and low release. The adsorption/desorption ability of the selected supports was monitored by HPLC-DAD and spectrophotometry assays. The chemometric approach, based on Principal Component Analysis and k-means clustering, identified three distinct clusters based on solid properties. Additionally, color analysis revealed similarities between residues treated with magnesium aluminium chloride and carbonate. The comprehensive analytical methodology employed for the adsorption/retention of GP polyphenols in lamellar solids is presented herein for the first time.

3D-printing bauxite residue/fly ash-containing geopolymers as promising metal sorbents for water treatment

Herein, we demonstrate for the first time the feasibility of employing significant amounts (up to 80 wt%) of unexplored industrial wastes (red mud and biomass fly ash) in the production of highly porous 3D-printed geopolymer lattices envisioned for wastewater treatment applications. This without compromising the mechanical performance of the geopolymers relative to those obtained using commercial precursors. The impact of the fly ash incorporation content in the fresh-state (calorimetric and reological characterization) and hardened-state (porosity and mechanical strength) properties of the produced structures was evaluated. Moreover, the influence of key printing parameters, including nozzle diameter and geometry alignment, on the resulting properties of the lattices was also evaluated. The most promising compositions were then evaluated as lead sorbents under continuous flow. The waste-based 3D-printed lattices showed remarkable adsorption ability reaching >95 % removal efficiency after 2 h. This sustainable strategy is in line with the United Nations sustainable development goals and the transition to a circular economy, reducing the consumption of natural resources and simultaneously contributing to reducing water pollution.

Chemical and thermal modification of geopolymer for efficient dye removal

In the pursuit of advancing sustainable wastewater treatment solutions in the industry, this study investigates the effect of chemical and thermal modifications on adsorbent geopolymer (GP) structure. Optimal conditions of sulfuric acid treatment and calcination temperature were determined to enhance the adsorption of the direct red dye 28 (DR28). Functional groups (FTIR), mineralogical composition (DRX), morphology (SEM-EDS), and physical properties (BET/BJH) were employed to study the effect of attack with H2SO4 and calcination on GP characteristics. The modified GP exhibited a high specific area (190 m2 g-1). Adsorption tests indicated that the Elovich model satisfactorily describes the kinetics, while the Sips model represents the isotherms. The maximum adsorption capacity achieved was 107.5 mg g-1. Remarkably, the adsorption capacity was doubled with GP regeneration, allowing reuse for three cycles. Furthermore, the selectivity profile uncovers a pronounced affinity hierarchy for dyes, with direct dyes manifesting a superior attraction, followed by acid, reactive, and disperse dye categories. Analyzing the efficiency of GPAT and comparing it with other GPs, it is evident that GPAT is an efficient and versatile adsorbent, featuring a simplified production process and requiring milder temperatures than those needed for activated carbon. Additionally, the cost-benefit analysis highlights geopolymers as a more economical and efficient alternative compared to conventional adsorbents.

Simultaneous removal of multiple metal(loid)s and neutralization of acid mine drainage using 3D-printed bauxite-containing geopolymers

The mining industry is one of the largest sources of environmental concern globally. Herein we report for the first time the application of highly porous 3D-printed sorbents containing high amounts (50 wt%) of red mud, a hazardous waste derived from the alumina industry, for the remediation of acid mine drainage (AMD). The sorption capacity of the inorganic polymers was initially evaluated for the simultaneous removal of five metal(loid) elements, namely Cu(II), Ni(II), Zn(II), Cd(II) and As(V) in synthetic wastewater. The effect of the initial concentration, pH and contact time were assessed, reaching removal efficiencies between 64% and 98%, at pH 4 and initial concentration of 50 mg L-1 of each cation, after 24 h of contact time. The 3D-printed lattices were then used for the remediation of the real AMD water samples, and the role of adsorption and acidic neutralization was investigated. Lattices were also successfully regenerated and reused up to five cycles without compromising their performance. This work paves the way for the use of an industrial waste derived from the production of alumina as raw material for the management of the hazardous AMD.

Additive manufacturing of geopolymers with hierarchical porosity for highly efficient removal of Cs. JOURNAL OF HAZARDOUS MATERIALS 2023;443:130161. [PMID: 36327833 DOI: 10.1016/j.jhazmat.2022.130161]

Geopolymers (GPs) have emerged as promising adsorbents for wastewater treatment due to their superior adsorption stability, tunable porosity, high adsorption capacity, and low-energy production. Despite their great promise, developing GPs with well-controlled hierarchical structures and high porosity remains challenging, and the mechanism underlying the ion adsorption process remains elusive. Here we report a cost-effective and universal approach to fabricate Na or K GPs with sophisticated architectures, high porosity, and arbitrary cation species exchange by means of additive manufacturing and a surfactant. The introduction of sodium lauryl sulfate (SLS) enhanced the porosity of the GP adsorbents, yielding NaGP-lattice-10%SLS adsorbent with a high total porosity of 80.8 vol%. Combining static and dynamic adsorption tests, the effects of morphology, surfactant content, and cation species on Cs⁺ adsorption performance were systemically investigated. With an initial Cs⁺ concentration of 900 mg/L, the printed NaGP exhibited a maximum Cs⁺ adsorption capacity of 80.1 mg/g, outperforming other adsorbents reported so far. The quasi-second-order fit of the NaGP adsorbent showed overall higher R² values than the quasi-first-order fit, indicating that the adsorption process was dominated by ion exchange. Combined with first-principles calculations, we verified that the content of water in the GP sod cages also affected the ion-exchange process between Na⁺ and Cs⁺.

Research and Application Progress of Geopolymers in Adsorption: A Review

Geopolymer is a porous inorganic material with a three-dimensional mesh structure, good mechanical properties, a simple preparation process (no sintering) and a low economic cost, and it is environmentally friendly. Geopolymer concrete has been widely used in the construction field, and many other studies have revealed that geopolymer will become one of the most promising inorganic materials with unique structure and properties. This paper provides a review of the development and current status of geopolymers and briefly explains the effects of material proportioning, experimental factors and activators on geopolymer performance. Because of the advantages of high specific surface area and high porosity, geopolymers could be used as adsorbent materials. This paper summarizes the research progresses of the adsorption of metal cations, anions, dyes, and gases by geopolymers, which emphasizes the geopolymer membranes in adsorption, and discusses the challenges and opportunities for the development of more efficient, sustainable and practical adsorption protocols.