Phosphoric Acid-based Geopolymers Research Articles

Improving the water resistance of phosphoric acid-based geopolymers by optimizing the Al/Si molar ratio method

Improving the water resistance of phosphoric acid-based geopolymers by optimizing the Al/Si molar ratio method

Valorization of ceramic sanitary waste into Resilient phosphoric acid-based geopolymers for sustainable construction: Thermal, mechanical, and microstructural properties

The construction industry's heavy reliance on conventional cement production contributes significantly to global carbon dioxide emissions, prompting the need for eco-friendly building materials. Geopolymers, synthesized from natural materials like clay and fly ash, offer a sustainable alternative to traditional cement. This paper investigates the development of phosphoric acid-activated geopolymers with sanitary ware waste (SWW) as aggregates, aiming to create high-performance, environmentally friendly building materials. Various particle sizes of SWW were incorporated into the geopolymer matrix, revealing a strong relationship between particle size and compressive strength. The inclusion of SWW improved compressive strength, with a notable 83 % increase at 30 % SWW content. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses highlighted the formation of new bonds in the geopolymeric gel, while scanning electron microscopy (SEM) showed microcracks and good adhesion between SWW particles and the geopolymer matrix. Thermal resistance tests demonstrated that SWW-reinforced geopolymers exhibited improved resistance to high temperatures compared to the reference geopolymer. XRD analysis of thermally treated geopolymers revealed the transformation of amorphous phases into stable crystalline phases. SEM/EDX mapping confirmed the presence of silica-rich phases, contributing to the materials' mechanical properties and thermal resistance. This study underscores the potential of SWW-based geopolymers as sustainable, high-performance building materials.

Mechanic performance of phosphoric acid-based geopolymer cured in an open environment

Mechanic performance of phosphoric acid-based geopolymer cured in an open environment

Enhancement mechanical properties of phosphoric-based geopolymer using aluminum dihydrogen phosphate

Phosphoric acid-based geopolymer (PGEO) is a acidic material, but the low strength and poor stability for the geopolymer synthesized with using fly ash limits its application and development. In this article, the aluminum dihydrogen phosphate (ADP) was introduced to form a composite activator to strengthen the mechanical strength of PGEOs synthesized from fly ash, and its hydration heat, workability, compressive strength, electrical conductivity (EC), and pHs were investigated, also the chemical and microscopic mechanism were also revealed. The results show that the geopolymerization heat was reduced after incorporating ADP activator. The workability were affected by the ADP content, the introduced ADP activator could improve the strength and long-term stability of PGEOs, and no compressive strength loss was found for the prepared geopolymer. The compressive strength reduced with EC raised with pH and, the Al–P existed in Al[OSi(P)]4 environment, and the geopolymer matrix composed of amorphous gels and crystalline compounds.

Wheat straw fibre based semi-IPN composite: Preparation and evaluation as a matrix for water and fertilizer release and in slope reinforcement

To improve the utilization rate of fertilizer and reduce environmental pollution, the effective management of water and fertilizer is extremely significant for the development of modern agriculture. Herein, using agricultural wastes (wheat straw fibre, WS) and phosphoric acid-based geopolymers (PGs) as eco-friendly materials, a novel wheat straw fibre composited polymer/PGs (WS-Po/PGs), was prepared by in-situ graft polymerization strategy, and a kind of nutrient-water carrier with semi-IPN was formed. Its structure and morphology were revealed by XRD, FT-IR, BET and SEM. Its water-retaining and controlled release behavior, and the nutrient release model were studied, while the effects on plant growth and loess slope of WS-Po/PGs were further investigated. The results illustrated that the obtained nutrient-water carrier had excellent water absorption (270.27 g/g) and salt tolerance (131.58 g/g) as straw fibres were mixed into polymer networks and formed semi-interpenetrating structures (semi-IPN). Comparing with controls, the WS-Po/PGs significantly improved the water retention capacity and N release longevity (30 d, 66.2%). Its nutrient release fitted the Fickian diffusion model (n < 0.5). Furthermore, the WS-Po/PGs could remarkably enhance the erosion resistance and stability of the loess slope, regulate the pH of the soil, and promote the germination rate of slope vegetation. In summary, by using agricultural wastes straw and loess as resources, the obtained WS-Po/PGs presented excellent slow-release behavior, salt tolerance and slope reinforcement function, and this kind of semi-IPN nutrient-water carrier could provide an insight for agriculture and slope protection.

Preparation of granite powder–based geopolymer by synergistic action of calcination and phosphoric acid

AbstractUsing the solid waste of granite powder (GP) to prepare green cementitious materials is of great significance for the sustainable development of the construction industry. In this study, a phosphoric acid–based geopolymer (PABG) was directly prepared from GP through a combination of phosphoric acid and calcination processes. Reaction mechanism of phosphoric‐activated GP is studied by techniques of X‐ray diffraction, thermal analysis, Fourier transform infrared spectroscopy, SE mode, and mercury intrusion porosimetry (MIP) taking calcination temperature, calcination time, and phosphoric acid as variables. The results indicated that the addition of 15 wt.% phosphoric acid and calcination at the temperature of 200°C for 90 min significantly increased compressive strength from 0.70 to 20.92 MPa. The calcination temperature was the most important factor in the synthesis of PABG using GP. The decrease of the peak value of mineral phase after calcination indicates that high temperature promotes the reaction between phosphoric acid and GP. According to the results of MIP, the gel generated by the reaction of phosphoric acid and GP refines the pore structure, which is conducive to the improvement of geopolymer properties. These research results provide a reference for the preparation of geopolymers directly using low pozzolanic active GP.

Insulating phosphoric acid-based geopolymer foams with water and high temperature resistance

This paper aims to determine the feasibility of phosphoric acid-based geopolymer highly porous foams elaborated by a surfactant induced mechanical foaming. The processing and consolidation parameters of the basalt fibers reinforced foams were determined. The influence of the aluminosilicate source on the synthesis of usable samples is reported, showing that the Si/Al ratio as well as the reactivity of the source is crucial to ensure a good consolidation. The effect of the Al/P composition of the geopolymer foam on its properties is also discussed. Two optimal formulations with very good properties (water and temperature resistance, mechanical strength, low thermal conductivity) could be established. Their working properties as well as their main physico-chemical characteristics, allowing to understand their formation mechanism were studied. Both withstood immersion in water and exposition to high temperatures. Their size may also be increased without any difference. Their insulating (61 to 75 mW.m−1K−1) and mechanical performances (80 to 190 kPa) are reported, as well as the study of their networks and microstructures.

Water adsorption and diffusion in phosphoric acid-based geopolymer using molecular modeling

Phosphoric acid-based geopolymer (PABG) is an environmentally friendly cementitious material. The adsorption and diffusion of water in PABG are investigated at the atomic scale. The adsorption isotherms are fitted by the Dubinin-Astakhov (DA) equation, and the adsorption isotherm is Type-V, qualitatively consistent with porous materials' adsorption characteristics. Adsorption isotherms and isosteric heats indicate that high temperatures weaken the attraction between water molecules and PABG, decreasing the adsorption amount with temperature. Water MSD suggests that the diffusion type is subdiffusion (one type of anomalous diffusion), verified by monitoring water molecules' diffusion trajectories, where the water molecule mainly fluctuates inside the pore and rarely jumps between pores. Effects of temperature and concentration on diffusion are analyzed. The anomalous diffusion exponent α, which reflects the diffusion rate, rises with temperature. Higher temperature enhances water molecule movement, and diffusion is accelerated. Higher water loading reduces α due to steric hindrance.

Manganese‐enhanced porous phosphoric acid–based geopolymer templated by carbon for efficient NH3‐SCR of NOx

AbstractGeopolymer‐based ceramics as catalysts or catalyst supports have attracted tremendous interests in recent years owing to their low‐cost and zeolite‐like structure characteristics. However, most of the reported works focus on alkaline‐based geopolymers, whereas the catalytic performance of acid based geopolymer has not yet been evaluated. This study aims to investigate the application potential of phosphoric acid–based geopolymer (PAG) for selective catalytic reduction (SCR) of NOx with NH3. To this end, the SCR reactivity of PAG and metal oxide (MnOx)‐loaded PAG were evaluated. Moreover, an activated carbon‐based hard template route was proposed for further enhancing the SCR reactivity of the PAG‐based catalyst. The as‐prepared catalyst under the optimal condition exhibited a high NO conversion greater than 85% in a wide temperature range of 250–350°C, which is among the top literature‐reported values, demonstrating its promising application prospect. A systematical X‐ray diffraction, X‐ray photoelectron spectroscopy, field emission scanning electron microscopy, Brunauer–Emmet–Teller, NH3‐temperature‐programed desorption, and H2‐temperature‐programed reduction spectroscopic analyses were also conducted to better understand the structure evolution of PAG under elevated temperature and the SCR catalytic mechanism of the acid‐based geopolymer catalysts. This study would provide valuable information on the potential application prospect of PAG and its modified form for efficient NOx removal.

Novel porous phosphoric acid-based geopolymer foams for adsorption of Pb(II), Cd(II) and Ni(II) mixtures: Behavior and mechanism

In this work, novel porous phosphoric acid activated geopolymer foams (abbreviated as PAG) with open cell structure are synthesized from a simple and effective process. Commercial metakaolin (MK) is used as raw material, hydrogen peroxide solution and Triton X-100 act as pore former and foam-stabilizer agents, respectively. The resultant PAG samples possess macropores around several millimeters and micro-cracks on geopolymer matrix. Different analytical instruments including optical microscope, X-ray diffraction, scanning electron microscopy equipped with energy-dispersive spectroscopy, Fourier transform infrared spectrometer, Brunauer-Emmett-Teller surface area measurement, etc. are applied to analyze the structural evolution. The obtained PAG is tested for heavy metals removal in unitary (Pb, Cd, Ni), binary (Pb–Cd, Pb–Ni, Cd–Ni) and ternary (Pb–Cd–Ni) metal solutions. The effect of pH on the simultaneous removal performance of Pb2+, Cd2+ and Ni2+ by PAG is studied. The maximum removal efficiency of Pb2+, Cd2+ and Ni2+ is achieved at pH = 7, and the selectivity sequences of the three metals adsorbed in ternary (Pb–Cd–Ni) metal solution is Pb2+ (11.99 mg/g)> Ni2+ (6.16 mg/g)> Cd2+(2.81 mg/g). The adsorption mechanisms are heavy metals exchanged with H+ in geopolymer matrix and surface complexation with the abundant –OH groups (Si–OH, P–OH, Al–OH) on PAG. The selectivity sequence can be ascribed to the difference of the hydrated heavy metals' radii. The heavy metals adsorption capacities of acid activated geopolymer foams are higher than that by alkali activated geopolymer monoliths reported in literature, suggesting its high potential application in wastewater treatment.

Water resistance of fly ash phosphoric acid-based geopolymer

Phosphoric acid (PA)-based geopolymers are different from alkali-activated materials. The PA-based geopolymers have good mechanical properties, but the related research is still less, especially the research concerning the durability of geopolymers has received less attention, which has brought some trouble to the engineering application. In this article, to further study the water resistance of PA-based geopolymer prepared using fly ash, the unconfined compressive strength tests were conducted to evaluate the water resistance. Meantime, the Scanning Electron Microscopy (SEM), SEM-EDS, SEM mapping, Mercury Intrusion Porosimetry, X-ray Diffraction, and Infrared Spectroscopy tests were used to reveal the mechanism of strength weakening of the geopolymers after soaking. The results show that the water resistance of the geopolymer first increased and then decreased with the increasing PA concentration. When the PA concentration was 50%, the geopolymer with the optimal PA concentration gave the best water resistance. The compressive strength was decreased significantly after soaking, and the strength first decreased rapidly and then reduced slowly with the soaking time increasing. At 7 days of soaking, the strength decreased rapidly with a decrease of 30–50%. After 7 days of soaking, the strength decreased slightly. After soaking, the at 180 days of soaking, the geopolymer specimens cracked except for the geopolymer with the optimal PA concentration. If the water stability of the acid-based geopolymer is not improved, it is difficult to meet the requirement of engineering application. The microscopic analysis shows that quartz and mullite did not participate in the polymerization, and the crystalline compounds formed in the geopolymer matrix, such as CaPO3(OH)·2H2O, CaHPO4, AlPO4, and CaPO3·OH, basically did not change after soaking, but some calcium-containing crystalline compounds leached after recrystallization after soaking in water, and the Si–O–P unit in the amorphous gel in the geopolymer hydrolyzed after soaking, also leading to the decrease the geopolymer strength.

Development of a new type of phosphoric acid based geopolymer/activated carbon composite for selective CO2 capture

• PAG was employed as novel AC binder to prepare high-performance CO 2 adsorbent. • PAG/AC composite exhibits superior CO 2 capacity than PAG. • PAG/AC composite exhibits superior CO 2 /N 2 selectivity than both PAG and AC. • Ultramicropore and surface modification of AC account for the performance. Herein, a phosphoric acid based geopolymer/activated carbon (PAG/AC) composite adsorbent was prepared for selective CO 2 /N 2 capture. The adsorbents exhibited hierarchical pore structures with ultra-micropores (approximately 0.58 nm) and mesopores (approximately 3.83 nm). The composite with 30 wt% of AC showed a much higher CO 2 adsorption capacity (17.6 cm 3 /g) than that of phosphoric acid-based geopolymer (6.8 cm 3 /g). Additionally, it had a high CO 2 /N 2 IAST selectivity of 12.7, which was greater than that of phosphoric acid-based geopolymer (3.9) and activated carbon (9.5). Spectral results confirmed that this was attributed to the AC ultra-micropores effect and the large interaction between phosphoric acid and AC during geo-polymerization.

Immobilization of uranium tailings by phosphoric acid-based geopolymer with optimization of machine learning

Immobilization of uranium tailings by phosphoric acid-based geopolymer with optimization of machine learning

Molecular dynamics simulation of phosphoric acid-based geopolymer

Phosphoric acid-based geopolymer (PABG) is a new amorphous cementitious material. PABG molecular dynamics (MD) simulation is carried out for the first time, using the modified Dreiding force field and the new macromolecular model. In this study, structural and mechanical properties of PABG, such as the bulk density, bond length, angle, radial distribution function (RDF), elastic modulus, and bulk modulus, are calculated by MD simulation. The bulk density is 1.85 ​g/cm3, close to 1.82 ​g/cm3 obtained in the experiment. The bond lengths of Si–O, Al–O, and P–O bonds and the angles of ∠OSiO, ∠OAlO, and ∠OPO agree well with the experimental values. The shape of the RDF curve can reflect short-range order and long-range disorder of the PABG structure. The elastic modulus is 33.42 ​GPa, close to 31.23 ​GPa measured by the nanoindentation experiment. The bulk modulus is 20.98 ​GPa, larger than the values obtained in the alkali-activated geopolymer (AAG) experiments. These results provide a reasonable basis for further PABG MD simulation research.

Potential of Cost-Effective Phosphoric Acid-Based Geopolymer as Photocatalyst for Dye Wastewater Degradation

Well recent study confirmed that surface Brønsted acid sites could evidently improve the formation of free hydroxyl radicals of semiconductors and thus enhanced the photocatalytic degradation activity. However, the intentional introduction of Brønsted acid sites on semiconductor surface was complex and expensive. In this study, the potential of low-cost phosphoric acid-based geopolymer (PAG) as photocatalyst for the degradation of dye was investigated for the first time. To this end, a batch of metakaolin-based PAGs with different P/Al ratios were prepared, and the photocatalytic degradation of Direct Blue-86 (DB-86) over PAGs was studied. Results showed that the process of phosphoric acid-activated geopolymerization endowed PAGs with redox ability by photoinduced holes and electrons, which suggested PAGs had photocatalytic activity. The photocatalytic degradation rate increased with increasing P/Al ratios, because the enhancement of the surface Brønsted acid deriving from non-tetrahedral P-OH groups improved the generation of free hydroxyl radicals. The PAGs reported here would be a promising candidate for dye wastewater treatment since the low-cost catalyst produces outstanding catalytic performance for their special structure.

Mechanical and microscopic properties of fly ash phosphoric acid-based geopolymer paste: A comprehensive study

Fly ash (FA) is a common industrial by-product, which is usually used as raw materials of alkali-activated geopolymer or cement additive. However, there are few studies on phosphoric acid-based geopolymer cement synthesized with FA. In this study, FA phosphoric acid-based geopolymer (FAPG) was prepared by using low-calcium FA as raw material and phosphoric acid (PA) as reactant at room temperature. Microscopic properties and geopolymerization mechanism were studied by X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, nuclear magnetic resonance instrument and Fourier transform infrared spectroscopy. The hydration characteristics were studied by isothermal calorimetry, and the thermal properties were explored by thermogravimetric analysis. Additionally, the setting time, compressive strength, pH and electrical conductivity of FAPG were measured. The results indicated that room-temperature cured FAPG paste activated with 50% PA and 0.3 liquid–solid mass ratio (L/S) yielded a maximum compressive strength during 0–90 days of curing. As curing time increased, the strength increased for FAPG with 50% PA, but increased at first and then scarcely increased for other FAPG pastes. The compressive strength decreased with L/S increasing. As curing time increased, the pH increased and electrical conductivity decreased. The initial and final setting time, and fluidity decreased with increasing PA concentration but increased with L/S increasing. The FAPG paste was a composite structure composed of crystalline and amorphous phase. The crystalline phase was composed of Brushite, Monetite and Berlinite, and the amorphous phase was composed of -Al-O-P-, -Si-O-P- and Si-O-Al-O-P- units. The average pore diameter of FAPG ranged from 37.38 to 64.44 nm. Heating to 1200 °C, FAPG paste presented four stages of mass loss. The total hydration heat increased with PA concentration increasing.

Robust Inorganic Daytime Radiative Cooling Coating Based on a Phosphate Geopolymer.

Daytime radiative cooling can spontaneously cool an object by reflecting sunlight and radiating heat in the form of infrared rays. Current daytime radiative cooling designs, including photonic structures and organic polymer-dielectric systems, are prone to age and fail under harsh conditions including high temperature, mechanical wear, and/or space irradiation. Here, an all-inorganic phosphoric acid-based geopolymer (PGEO) paint was developed and showed robust radiative cooling performance. This versatile suspension paint can be applied directly to diverse surfaces through scalable techniques such as spray coating and brushing. This inorganic coating possesses a high average hemispherical infrared emissivity >0.95 and reflects nearly 90% of solar irradiance. We attributed this excellent spectral selectivity of the PGEO coating to its unique inorganic geopolymer network (-Si-O-Al-O-P-O-), which settled the vibration intensity in a suitable range (0.2 < k < 1) and enabled multimode vibration. Moreover, this inorganic coating exhibits good comprehensive performance in terms of heat endurance, mechanical strength, and resistance to intense proton radiation, showing its promising applications in spacecraft, buildings, and communication base stations.

Undehydrated kaolinite as materials for the preparation of geopolymer through phosphoric acid-activation

This work focuses on the geopolymerization of undehydrated kaolinite in place of the more commonly used dehydrated kaolinite via phosphoric acid-activation. The results showed that the compressive strength, microstructure, and chemical composition of acid-activated undehydrated kaolinite were greatly affected by the concentration of phosphoric acid. When kaolinite was acid-activated by 10 mol/L and 12 mol/L phosphoric acid, metavariscite and geopolymer with P–O–Al network were obtained; but the products possessed porous and inhomogeneous microstructure, which exhibited low compressive strength. When kaolinite was acid-activated by 14 mol/L phosphoric acid, geopolymer dominant with Si–O–P–O–Al networks was synthesized, which had compact and dense microstructure. The compressive strength of the geopolymer product was greatly improved. These results demonstrate the feasibility of using undehydrated kaolinite as the starting material for the preparation of phosphoric acid-based geopolymer. The findings of this study have meaning not only for extending the application field of kaolinite but for reducing the energy input in geopolymer preparation.

Fire resistance of phosphoric acid-based geopolymer foams fabricated from metakaolin and hydrogen peroxide

In this research, phosphoric acid-based geopolymer foams (PAGFs) are fabricated from metakaolin and phosphoric acid with hydrogen peroxide as a foaming agent. Properties of PAGFs are characterized by a series of tests, including porosity, dry bulk density, compressive strength, thermal conductivity, fire resistance, XRD and SEM. The porosity and dry bulk density of PAGFs are tightly dependent on the hydrogen peroxide content, which further influence the compressive strength, thermal conductivity and fire resistance. Moreover, the excellent high temperature stability of PAGFs is beneficial to the thermal conductivity and fire resistance. After 2 h fire resistance tests, the reverse-side temperatures except the PAGFs with 4% mass fraction of hydrogen peroxide still maintain around 220 °C. Therefore, PAGFs with extraordinary fire resistance have great potential for fire protection.

Synthesis, thermal properties and electrical conductivity of phosphoric acid-based geopolymer with metakaolin

In this work, kaolin was used to prepare a geopolymer from a phosphoric acid solution. Microstructural properties were investigated by X-ray powder diffraction, while thermal properties were evaluated by differential thermal analysis and thermogravimetry. Finally, the electrical conductivity of the geopolymer and its dielectric properties were investigated.The results showed that the onset temperature of crystallization of the zeolite phase occurred at 180 °C. This phase was converted into phosphocristobalite phase at 300 °C and persisted until 1400 °C. From the temperature of 700 °C, a new crystalline phase was observed: the tridymite SiO2.The amount of phosphocristobalite and tridymite crystals reached a maximum at approximately 1100 °C, then, at 1400 °C, the X-ray diagram showed that the peak presented a weak intensity due to the partial dissolution of two solid crystalline phases: tridymite and cristobalite. The electrical conduction properties of the geopolymer indicated first a very low solid-state conductivity (σ ≈ 10−10 S.cm−1), and then above 625 °C, the conductivity began to rise rapidly, reaching 10−7 S.cm−1.