MAPS Laboratory
Materials’(Ma) Process(P) - Structure(S) correlations Laboratory
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Department of Metallurgical and Materials Engineering
Indian Institute of Technology Patna (IIT Patna)
Environmental remedition of dye adsorption
Pollution has become an unavoidable reality in modern life. Among all forms of pollution, water pollution is one of the most concerning, as water is considered the source of life and the most vital liquid in our ecosystem. Organic contaminants from various sources, such as the textile, paint, and chemical industries, pollute water bodies and pose constant threats to our quality of life. Every year, tons (∼10 ) of dyes and pigments are produced worldwide and used in cosmetics, pharmaceuticals, paper, plastic, textile, food, leather, and other industries. Of these, about 15% are released into the environment, mostly into water bodies as effluents. Many of these dyes are toxic and have been reported to be mutagenic and carcinogenic to aquatic organisms. Additionally, they negatively impact photochemical activities by reducing light penetration in aquatic environments. Some dyes are also known to cause irreparable damage to genetic material, human cells, eyes, and skin
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Figure: Dye usage, pollution and their removal by adsorption
Importance of dye adsorption?
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Effectively removes both organic and inorganic dye pollutants from water, making it a versatile solution
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Ability to treat highly concentrated dyes in a short time
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unlike photocatalysis, adsorption does not depend on sunlight, allowing it to be implemented under various environmental conditions
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cost-effective and eco-friendly approach, making it a desirable choice for sustainable water treatment applications
​Our previous works on a few dye adsorbents
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Calcia-Stabilized Zirconia Nanoparticles
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Yttria-Stabilized Zirconia Nanoparticles
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Mg–Al-Layered Double Hydroxide (LDH)
​Calcia-Stabilized Zirconia Nanoparticles
The domain of dye adsorption using zirconia systems remains largely unexplored, with its full potential yet to be realized. Unlike previous studies, where zirconia was primarily incorporated into composites for adsorption experiments, we focused on doping zirconia with 4 mol.% of CaO to investigate its dye adsorption capabilities. CaO-doped tetragonal ZrO nanoparticles have proven to be excellent adsorbents for anionic dyes.
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CaO-doped tetragonal ZrO2 nanoparticles have proven to be excellent adsorbents for anionic dyes​ for the following reasons:-
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•Achieved a maximum adsorption capacity of 186 mg/g for the toxic azo dye Congo Red
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•High surface area (113 m2/g) enables rapid dye removal (>85% within five minutes)
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•Adsorption follows a pseudo-second-order kinetic model and fits well with the Langmuir isotherm
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•CaO doping enhances chemical interactions through ion-exchange, significantly improving adsorption efficiency.
•Demonstrated effectiveness in environmental remediation under real (Ganges) water conditions
•Compared to commercially available yttria-stabilized ZrO2, CaO-doped ZrO2 exhibits superior dye adsorption performance
Figure:Congo red dye removal by adsorption using 4 mol.% CaO-doped ZrO2 (4CaSZ nanoparticles)
Figure:Schematic representation of the possible reaction mechanism for the adsorption of congo red onto 4CaSZ nanoparticles
Further works on Calcia-stabilized zirconia
The impressive adsorption potential of 4 mol.%CaO-doped ZrO2 (4CaSZ) nanoparticles has motivated us to explore the varied doping of CaO(0, 7, 10, and 16 mol.%) and the role of phase stabilization (monoclinic, tetragonal and cubic) in zirconia systems.
•Achieved a record-high adsorption capacity of 760 mg/g for Congo Red with 16 mol.% CaO-doped ZrO2 (16CaSZ)
•The 16CaSZ nanoparticles exhibited the fastest dye removal kinetics and excellent adsorption (~99%) in simulated industrial effluent
•Consistent adsorption performance across pH levels from 2 to 10, even in the presence of various anions (Cl-, NO3-, SO42-)
•Remarkable adsorption is attributed to phase-pure cubicity, high oxygen vacancy content, and a large surface area
•Structural and spectroscopic analyses of post-adsorption products indicate a chemisorption-based process
Figure:Influence of varied CaO doping on ZrO2, highlighting the variations in phase transition and adsorption capacity of congo red dye
Yttria-Stabilized Zirconia Nanoparticles
The previous work demonstrated that doped cubic ZrO2can serve as an efficient dye adsorbent. However, commercially available 8 mol.% Y2O3-stabilized zirconia (8YSZ) has shown no signs of adsorption. Intrigued by this unexpected behavior, we synthesized 8YSZ in the lab by optimizing the process parameters similarly to those used for CaSZ synthesis
•Lab-synthesized 8YSZ, with optimized parameters, achieved a remarkable adsorption capacity of ~550 mg/g for Congo Red while commercial variant showed no adsorption
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•Success can be attributed to size refinement (~6 nm), retention of phase-pure cubicity, enhanced surface area (155 m²/g), and generation of abundant oxygen vacancies
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•The adsorption efficacy was validated through tests conducted in real river water, mixed ion solutions, and across a range of pH levels (3–11), along with successful regeneration via thermal and chemical methods
Figure:Mechanism of congo red adsorption on Syn-8 mol.%yttria-stabilized zirconia (8YSZ) nanoparticles
Mg–Al Layered Double Hydroxide (Mg-Al LDH)
Layered double hydroxides (LDHs), specifically hydrotalcite [Mg6Al2(OH)16CO3•4H2O] consist of metal hydroxide layers balanced by anions.These clay-like materials are well-known for their adsorption efficiency due to their ion-exchange and intercalation capabilities. However, traditional reports indicated that their adsorption capacities were quite low. To address this limitation, LDHs have typically been modified using various compounds, developed into composites, or occasionally subjected to calcination to convert them into Mg-Al oxides or spinels. Despite these modifications, LDHs possess unique structural and chemical properties that make them excellent adsorbents.
Optimizing synthesis methods can significantly enhance their performance without requiring the addition of other materials. One effective approach is to increase the proportion of trivalent aluminum ions (Al )while maintaining a Mg/Al ratio of approximately 2 instead of the conventional ratio of 3.
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•Successfully synthesized and investigated the adsorption behavior of pristine LDH with a Mg/Al ratio of ~2
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•Achieved rapid dye removal (~100% in just 2 minutes) and recorded a maximum adsorption capacity of 207 mg/g for amido black dye
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•The mesoporous structure and net positive charge in the aqueous medium likely contributed to enhanced adsorption efficiency
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•The demonstrated optimal synthesis procedure enables LDHs to be effective for dye adsorption without the need for additional modifications
•Post-adsorption analyses confirmed the chemical interactions and intercalation of dye molecules within the LDH lattice, resulting in an increased d-spacing
Figure:Schematic illustrating LDH adsorbing amido black dye through ion exchange and intercalation
Remarkable dye-adsorption capability of Mg-Al LDH
The successful adsorption of the anionic amido blackdye through ion exchange and intercalation has motivated us to utilize Mg-Al LDH as an anionic dye adsorbent. Our goal was not only to assess the adsorption of individual anionic dyes but also to evaluate the LDH's ability to adsorb multiple anionic dyes, both individually and in mixed forms. We aimed to demonstrate the efficacy of Mg-Al LDH as an efficient adsorbent for multi-anionic toxic dyes.
Remarkable adsorption capacity is obtained which is as follows
•The dye adsorption capability of LDH was tested with various anionic dyes, including reactive, azo, and acid dyes, to mimic real wastewater conditions
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•Achieved ~100% dye removal for all eight dyes, both individually and in mixed form, in just two minutes
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•Chemisorption of dye constituents onto Mg-Al LDH occurred through ion-exchange reactions
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•Formation of guanidinium aluminum sulfate on Mg-Al layered double hydroxide was observed
Figure:Adsorption of multi-anionic toxic dyes,both individually and in mixed forms by LDH
Figure:UV–Visible spectroscopy plots for the adsorption ofmulti-anionic toxic dyes