Geopolymer Powder Research Articles

A renewable bifunctional structural supercapacitor using the recycled geopolymer membrane and MnO2/CNTs electrode

A bifunctional supercapacitor based on the recycled montmorillonite geopolymer membrane and MnO2/CNTs composite electrodes was designed and assembled. The recycled geopolymer was prepared from recycled montmorillonite geopolymer powder and alkali activators and used as a solid electrolyte skeleton, with a maximum compressive strength of 30.6 MPa after 28 days of curing, which is comparable to the strength of the initially polymerized geopolymer. The MnO2/CNTs electrodes were prepared by electrodeposition method, and the electrode materials containing 2 wt% CTAB and 1 wt% CNTs had the best area specific capacity of 3310 mF cm−2 at a current density of 1 mA cm−2. The regenerated geopolymer electrolyte framework was injected with 0.5 M Na2SO4 and assembled with MnO2/CNTs electrode to form a structural load-bearing supercapacitor, which had a specific capacity of 2094.4 mF cm−2 at a load of 15 MPa, with a capacity retention rate of 65.43 % after 10,000 charge/discharge cycles.

Use of geopolymers as tunable and sustained silver ion release mediums

Silver was incorporated up to 3.4% (w/w) into the geopolymer structure via precipitation as Ag2O by dispersing the geopolymer powder in an aqueous solution of AgNO3. The precipitates were mainly located in the fine pores within the nanoparticles of the geopolymer network. The fine pores enabled the formation of very fine precipitates, mainly between 2 and 5 nm. The silver-incorporated geopolymer was found to have a sustained Ag+ release that can be tuned down by a thermal treatment, e.g., calcination. The Ag+ release amount could be reduced by about 30-fold after calcination at 850 °C. Calcination reduces the specific surface area, causes shrinkage, and makes the geopolymer structure less pervious. The size of the precipitates remains stable even up to 1050 °C, despite a large amount of sintering-related shrinkage. These results suggest that geopolymers could be a tunable Ag+ source for various antibacterial applications.

Synthesis of geopolymer powder and beads based on red clay waste for the adsorption of methyl orange dye from aqueous solutions: Characterization, application of response surface methodology, and cost analysis

The current research focuses on the valorization of red clay waste (RCW) to develop alumino-silicate geopolymer binders (GPP) and geopolymer spheres obtained from GPP powder modified with sodium alginate (Alg/GPP). GPP and Alg/GPP were applied in the environmental field for the retention of methyl orange (MO) from an aqueous solution. The raw material and the synthesized geopolymers were characterized by various physico-chemical methods. The results of XRF, XRD, and FTIR confirmed the successful synthesis of GPP and Alg/GPP, while the SEM/EDX findings revealed the homogeneous surface of the adsorbents. A significant specific surface area was detected for GPP (73.56 m2/g) and Alg/GPP (91.24 m2/g) with a high cation exchange capacity around 122 meq/100g for GPP and 185 meq/100g for Alg/GPP. The removal process was performed using the response surface methodology according to the Box-Behnken design, optimizing the retention efficiency of MO by different factors, including temperature, initial concentration, solution pH, and contact time. The obtained data was treated through the analysis of variance (ANOVA) and fitted by a quadratic polynomial model based on multiple regression analysis. In an acidic medium at 45 °C, the optimal conditions for MO retention were estimated to be 120 mg/L of MO concentration in 55 min using GPP and 180 mg/L of MO concentration in 20 min using Alg/GPP. The pseudo-second-order kinetics were more appropriate for describing the MO removal onto GPP and Alg/GPP adsorbents. The Langmuir model identified a high retention capacity of MO around 94.78 mg/g via GPP and 224.85 mg/g via Alg/GPP. The thermodynamic data confirmed that the elimination of MO dye onto GPP and Alg/GPP adsorbents was endothermic, favorable, and spontaneous. This study provided insights into the valorization of composite materials based on solid waste in dye retention, which can potentially be employed in wastewater treatment.

Insight into adsorption properties and mechanism of geopolymer adsorbents with inherent alkali release for tetracycline

The crux to practical application of geopolymer adsorbents for antibiotics that are easily protonated and deprotonated is to clarify the dynamic adsorption mechanism of geopolymer with intrinsic alkaline release. The adsorption properties, adsorption mechanism, adsorption-desorption cycle and waste adsorbent regeneration based on the geopolymer adsorbent for adsorbing tetracycline under the spontaneous dynamic pH conditions were systematically investigated by experiment, characterization and density functional theory. The results confirmed that the structures of tetracycline depended on dynamic pHs of adsorption systems changed by geopolymer adsorbent. The electrostatic interaction assisted by hydrogen-bonding and n-π interaction dominated the adsorption process when the dynamic pHs were less than 7. And the hydrogen-bonding and n-π interaction provided the possibility of weak adsorption effect in highly alkaline environments. The geopolymer powder exhibited outstanding adsorption efficiency (∼95.62%, 30 min) due to the strong electrostatic adsorption between electronegative skeleton of geopolymer and zwitterions species tetracycline under dynamic pH range of 4–6.3 and fitted the pseudo-second-order model. The outstanding competitive adsorption properties in NaCl solution, adsorption (4 times)-desorption (3 times) cycle properties and regenerative property of waste adsorbent were exhibited. The mechanism study based on the dynamic pHs which is closer to actual conditions can provide important reference for practical application of easy preparation and low cost geopolymer adsorbents.

Flexural Strength and Porosity of NaOH-Treated Maize Stalk Cellulose-Fibers-Reinforced Geopolymer Composites

This study characterizes the flexural strength and porosity of NaOH-treated maize stalk cellulose-fibers-reinforced geopolymer composites. Flexural strength tests are conducted, and the fracture surfaces of the composite and geopolymer powder are observed using a scanning electron microscope (SEM). Moreover, porosity analysis is also performed using Image J software from SEM images. The formation of geopolymer is confirmed using X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The addition of 1.5 wt% of NaOH-treated maize stalk cellulose fibers improves flexural strength by 2.4 times. The results show that the main failure mechanisms, namely fiber breakage, fiber pullout, and debonding of the fiber and matrix, can increase flexural strength and reduce failures during service life. During the analysis for fiber and particle pullout, SEM images under 25^2 pixels of pore areas are not considered, and an average porosity of 36.7% is achieved.

Physico-mechanical and microstructural properties of waste geopolymer powder and lime-added semi-lightweight geopolymer concrete: Efficient machine learning models

Physico-mechanical and microstructural properties of waste geopolymer powder and lime-added semi-lightweight geopolymer concrete: Efficient machine learning models

Shrinkage, compressive and bond strengths of alkali activated/cement powder for alternative coating applications

This paper reports the properties of a novel coating material produced from alkali-activated/cement powder (AACP), including setting time, strength development, drying and autogenous shrinkages, and bond strength of one-part AACP paste-coated reinforcing steel bars in concrete. The AACP paste was prepared by activating a mixture of dry geopolymer powder (GPP), Portland cement (PC), and silica fume (SF) with tap water and 2 M sodium hydroxide solution. The effect of PC replacement, sodium silicate-to-sodium hydroxide solution (SS-to-SH) ratio, and pre-curing temperature in the production of GPP on the properties of AACP paste were also investigated. Test results showed that the incorporation of FA and PC activated with an SS-to-SH ratio of 2.0 for the production of GPP decreased their setting time of fresh one-part AACP pastes, whereas their strength development marginally increased. Furthermore, the increasing PC content and SS-to-SH ratio had an adverse effect on drying and autogenous shrinkages. However, the pre-curing temperature had a marginal effect on their shrinkages. In addition, one-part AACP paste-coated reinforcing steel bars positively affected the bond strength of reinforced concrete, especially for the GPP produced by FA without PC. The increased reaction products at the contact zone could assist in improving their bond strength. It can be recommended that the use of FA without PC activated with a low SS-to-SH ratio in the production of GPP would be beneficial in improving shrinkage and bond strength while providing high equivalent substrate stiffness (ks).

Utilizing waste geopolymer powder as partial cement replacement for sustainable cement mortar: Micro-macro properties and modification

The increasing application of alkali-activated geopolymer materials generates more geopolymer waste, but the reuse of geopolymer waste has been given less consideration until now. The ground waste geopolymer powder (WGP) has the potential to be used as supplementary cementitious material. Therefore, this study examined the characteristics of cement-based materials with WGP as a substitute for particle cement. The mortar samples (70.7 × 70.7 × 70.7 mm) were prepared for strength and transport properties measurement. The findings indicated that WGP ground from various geopolymer wastes mainly contained C–(N)–A–S–H, mullite, SiO2 or CaCO3. Substituting WGP for partial cement negatively impacted the paste micro-structure and increased the percentages of harmful and more harmful pores. The addition of WGP reduced the mechanical strength and increased the transport properties, and the maximum capillary absorption coefficient of 30% WGP mixed mortar was 154.0% higher than that of reference mortar without WGP. When WGP replacing level was the same, the water absorption of mortar incorporating WGP ground from FA-based geopolymer waste was obviously lower than that of mortar with WGP ground from GGBS-based geopolymer waste, because WGP ground from FA-based geopolymer waste contained some un-treated FA particles which benefited filler effect and pozzolanic activity. The addition of active admixtures could enhance the performance of WGP blended mortar. Specifically, the mortar containing 20% WGP and 10% silica fume/metakaolin had similar strength and lower transport properties compared with reference mortar, and the properties of WGP blended mortar were improved with the mix of Nano-SiO2.

Durability properties of novel coating material produced by alkali-activated/cement powder

This paper presents a feasibility study on the use of alkali-activated/cement powder (AACP) paste as a potential coating material for improving the durability of structures and protecting buildings exposed to marine environments. The AACP was synthesized by geopolymer powder (GP), Portland cement (PC), and silica fume (SF). The water-to-binder ratio of 0.45 and sodium hydroxide solution of 2 M were used to activate the reaction products of the AACP paste. The experimental tests consisted of the retained compressive strength and weight change after exposure to 5 % sulfuric acid (H2SO4) solution, 5 % magnesium sulfate (MgSO4) solution, and tap water (H2O), and chloride migration coefficient (RCM). The corrosion probability of concrete reinforcement with surface treatment of deformed bar (DB) using the half-cell potential (HCP) test was also evaluated. Test results showed that the AACP paste exhibited superior durability to PC paste, as evidenced by its relatively low strength loss and weight change. In addition, the chloride diffusion coefficient of AACP pastes was 32.7 to 77.6 times lower than that of PC paste. For the corrosion probability of concrete reinforcement, the average HCP values of the AACP paste-treated-deformed bar were lower than those of the no-treated or PC paste-treated-deformed bar, especially for the AACP paste prepared by GP without PC.

Preparation of Al2O3-2SiO2/geopolymer powder by hydrolytic sol-gel method and its activity characterization and research on the reaction mechanism

Herein, we report the application of sol-gel method for the preparation of a new type of highly active Al2O3-2SiO2 geopolymer precursor powder. The newly synthesized geopolymer precursor powder was characterized by SEM, XRD, TG, FTIR and MAS NMR. Experimental results showed that all the geopolymer precursor powders prepared by this method exhibited amorphous crystal structure and FTIR absorption peaks were consistent to typical aluminosilicate. TG analysis showed that G1-0-35 prepared with pure water as the aluminum source solvent had higher weightlessness rate, and with the increase of water quantity, the layered structure appeared, the resonance peak of hexacoordination Al(VI) was enhanced and the coordination of silicon was changed. ICP test results showed that the G1-0-35 precursor powder with pure water as the aluminum source solvent dissolves more quickly in the NaOH, and the relative crystallinity was the highest (84%) after alkali activation. The changes in conductivity of different geopolymer precursor powders during the reaction at different temperatures and the changes in the concentration of aluminum and silicon ions with time in the geopolymer reaction were explored, which showed that the activity of geopolymers powders increased with increasing the amount of water. The geopolymer precursor powder prepared in this study are in line with the requirements of green production, and prompts great advantages in the study of geopolymer reaction mechanism.

Strength and Microstructural Analysis of Geopolymer Prepared with Recycled Geopolymer Powder

Strength and Microstructural Analysis of Geopolymer Prepared with Recycled Geopolymer Powder

Preparation, Characterization, and Application of Metakaolin-Based Geopolymer for Removal of Methylene Blue from Aqueous Solution

Metakaolin-based geopolymers are aluminosilicate materials that can be used as cationic dye adsorbents in aqueous system treatment. Our aim in this paper is to study the ability of geopolymer powder produced from metakaolin and alkaline activators to act as an adsorbent to remove methylene blue (MB). The solid materials were systematically analyzed by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectrometery (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and the point of zero charge. XRF, FTIR, XRD, SEM, and EDX analyses confirmed the formation of a geopolymer composite by geopolymerization reaction. The influence of various experimental factors such as geopolymer dosage, pH, initial dye concentration, contact time, and temperature was assessed. Adsorption isotherms were evaluated by Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherms. Kinetics data were studied using pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. The thermodynamic parameters, namely, Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), were determined. The results indicated that the maximum decolorization was found in high pH values. The collected isotherm data were best fitted by the Langmuir isotherm, and the maximum adsorption capacity of dye onto the geopolymer was 43.48 mg/g. The experiment kinetics followed the pseudo-second-order kinetic models. The thermodynamic results demonstrated that the adsorption of the obtained material occurs spontaneously as an endothermic process. The results confirmed that the prepared adsorbent can be used for remediation of water contaminated by MB dye.

Strip-like wet bottom slag-based geopolymer as an adsorbent for removal of heavy metal ions

The strip-like wet bottom slag-based geopolymer mixed with PES-NMP solutions, which used sodium hydroxide and sodium silicate as alkali activators, wet bottom slag as base materials respectively, were prepared by phase transition method. The as-prepared WBS geopolymer powder and strip-like adsorbents were systematically characterized by XRF, BET, XRD, SEM and heavy metal adsorption respectively. The experimental results presented that wet bottom slag had the potential to use as the base materials of geopolymer, which can form the amorphous structure, higher surface area and a bigger pore volume. That makes the adsorption of heavy metal to come true. When the heavy metal amount as 20 mg/L of each Fe2+ and Cu2+ ions, 40 mg/L of Mn2+, the as-prepared WBSG-PES-NMP strips showed the highest absorption capacity of 56.8%, 63.2% and 88.4% respectively.

Printability, accuracy and strength of geopolymer made using powder-based 3D printing for construction applications

Abstract The authors of this study have recently succeeded to develop geopolymer materials using slag only formulations for the requirements and demands of commercially available powder-based 3D printers. In this study, the formulation is extended to fly ash and slag combinations so that to expand the scope of geopolymer materials that can be used in the commercially available powder-based 3D printers for construction applications. The quantitative influence of fly ash content on the printability characteristics (i.e., depositability and wettability) of the geopolymer powder, as well as the linear dimensional accuracy and compressive strength of the printed specimens were investigated. The effect of type of alkaline solution used for post-processing on the linear dimensional accuracy and compressive strength of the post-processed specimens were also evaluated. The results indicated that the increase in fly ash content had no effect on the powder depositability, but adversely affected the powder wettability, linear dimensional accuracy and compressive strength of the printed specimens. The minimum slag content required to prepare fly ash/slag blended geopolymer powder for powder-based 3D concrete printing process is 50 wt%. The post-processing significantly increased the compressive strength. The post-processed specimens printed with 50 wt% slag/50 wt% fly ash powder exhibited a 7-day compressive strength of up to 25 MPa, which is sufficiently high for many construction applications.

The effect of water binder ratio on strength development of class C fly ash geopolymer mortar prepared by dry geopolymer powder

The use of geopolymer binder as cement replacement material can reduce the amount of carbon dioxide gas produced during the Portland Cement manufacturing process. However, the main issue of geopolymer binder is in the mixing process of sodium silicate and NaOH which requires specialized knowledge and strict supervision. This paper reports the effect of water binder ratio on strength development of fly ash geopolymer mortar using dry geopolymer powder. Fly ash with high calcium content was used as primary material. The dry geopolymer powder was prepared by wet mixing method which was made by drying a mixture of NaOH solution and limestone for 24 hours. The variations of water to binder ratio were 0.30, 0.35, 0.40, 0.45, and 0.50. Strength properties were measured by compressive strength at the age of 7, 14 and 28 days. The results showed that the water binder ratio significantly affect the strength development of geopolymer mortar prepared by dry geopolymer powder. The water binder ratio of 0.40 gives the highest compressive strength of 10.3 MPa at 28 days. This suggests that the use of dry geopolymer powder on geopolymer mortar production can overcome the difficulties of geopolymer mortar mixing on site.

Porous fly ash-based geopolymer composite fiber as an adsorbent for removal of heavy metal ions from wastewater

This paper describes a simple and effective process for fabricating geopolymer-polymer composite fiber. The fiber is synthesized by mixing geopolymer powder with Polyethersulfone (PES) – N-Methyl-2 pyrrolidone (NMP) solution and the slurry was extruded then transformed into a fiber by phase inversion method. The fiber is constructed of PES and fly ash-based geopolymer (FAG) particles with porous structure. Analysis of the pore structure of fiber revealed that BET surface area is 168.30 m2/g. In addition, the adsorption capacity of heavy metal ions on geopolymer composite fiber follows the order of Pb2+ > Cu2+ > Cd2+ > Ni2+. This work provides a convenient, low-cost and environmental friendly adsorbent for removing heavy metal ions from waste water.

Lattice-shaped geopolymer catalyst for biodiesel synthesis fabricated by additive manufacturing

This work presents the results of a preliminary study in which a sodium aluminosilicate geopolymer powder was shaped into a lattice component by additive manufacturing and successfully employed as a structured heterogeneous catalyst for biodiesel production. The processing and the structural characterization of the 3D printed body and the chemical conversion tests are described and discussed.

Metakaolin Based Geopolymer from Thailand as an Adsorbent for Adsorption of Multi- and Mono- Cations from Aqueous Solution

Waste management and water quality are two main problems nowadays. Geopolymer material has efficiency for adsorbing the ions from wastewater. In this research, the metakaolin based geopolymer was studied and used as an adsorbent to remove heavy metal ions. Moreover, the factors which affect adsorption process of heavy metals on geopolymer materials were investigated. The kaolin as used in this research was from Thailand. The metakaolin geopolymer was synthesized by mixed raw materials with an alkaline solution. The metakaolin geopolymer was washed and sieved through 100 mesh. The produced metakaolin geopolymer powder was used as an adsorbent. The XRD results showed a highly amorphous structure in obtained metakaolin geopolymer. Moreover, the BET surface area of metakaolin and geopolymer particles were 9.83 m2/g and 20.36 m2/g, respectively. The parameters of adsorbent amount, initial pH, time of shaking, temperature and initial metal ions concentration on the removal potential of geopolymer were studied. In addition, the multi-and mono-cations solution were demonstrated to compare the efficiency of each heavy metal ions. The results showed that the amount of Pb2+, Cu2+, Cd2+, and Ni2+ions adsorbed onto metakaolin geopolymer increased with an increasing contact time, pH, temperature and amount of geopolymer. It is concluded that Pb2+, Cu2+, Cd2+, and Ni2+ions in aqueous solution are efficiently removed by metakaolin geopolymer which could be applied as a low cost and good alternative for wastewater treatment.

Removal of Pb<sup>2+</sup>, Cu<sup>2+</sup>, Ni<sup>2+</sup>, Cd<sup>2+</sup> from Wastewater using Fly Ash Based Geopolymer as an Adsorbent

This work aims to evaluate the effectiveness of fly ash based geopolymer powder as an adsorbent for heavy metals in aqueous solution. The structure of synthesized geopolymer was found to be highly amorphous due to the dissolution of fly ash phase. Moreover, the fly ash geopolymer powder has higher surface area compares to original fly ash with specific surface area of 85.01 m²/g and 0.83 m2/g, respectively. For this reason, the geopolymer powder has much higher removal efficiency compared to the original fly ash powder. The removal efficiency was affected by contact time, geopolymer amount, heavy metal initial concentration, pH, and temperature. The four heavy metals were chosen (Pb2+, Cu2+, Ni2+, Cd2+) for adsorption test. The highest heavy metal removal capacity was obtained at pH 5. The geopolymer powder adsorbed metal cations in the order of Pb2+>Cu2+>Cd2+>Ni2+. In addition, Langmuir model is more suitable for fly ash geopolymer powder adsorption of heavy metal ions in aqueous solution than Freundlich model. The results showed that the fly ash geopolymer powder has high efficiency for removal metal which could be employed excellent alternative for wastewater treatment.

Thermal Characterization of Metakaolin-Based Geopolymer

Thermal characterization of geopolymer powder was investigated at room and elevated temperatures. The physical, chemical and mass change with respect to various temperatures have been studied. The physical properties such as density, porosity, and particle size were analyzed in geopolymer powder. The chemical and phase compositions were determined by x-ray fluorescence. The surface images of solid blocks of geopolymer were examined at room and elevated temperatures using scanning electron microscopy. Thermal expansion, shrinkage, and mass loss behavior towards the elevated temperatures were investigated by differential scanning calorimetry (DSC). The endothermic peak arising in the DSC curve is due to evaporation of water, chemical, gases and weight loss.