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co2 adsoption 2111mm14 (1) (1)

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: 2111MM14
Research Paper
Alkali-treated titanium dioxide as adsorbent for CO2 capture from air
Journal : Microporous and Mesoporous Materials
Citations : 23
http://dx.doi.org/10.1016/j.micromeso.2014.10.013 (2014)
1. Introduction
2. CO2 adsorbent material
3. Sample Preparation
4. CO2 adsorption capacity
5. Results
6. Conclusion
What is necessary of CO2 adsorption from atmospheric air ?
Carbon dioxide (CO2) among other air pollutants is a major culprit to the greenhouse gases that is fueling global warming.
Among the greenhouse gases, CO2 contributes more than 60% to global warming because of its huge emission.
Example of CO2 adsorbents
 Metal oxides
 Zeolites
 Silicas
 Metal organic frame work(MOF)
Metal Oxides (TiO2)
Criteria for selection of TiO2:
1.high adsorption capacity
2.high stability, abundant availability and inexpensive cost
3. titanium dioxide has attracted considerable attention for its potential applications in
photocatalysis, solar cells electronics and sensors
4. titanium-based materials with high specific surface area and ion-exchangeable ability show
exciting prospects for CO2 adsorption.
Preparation for modified TiO2 samples
Materials Required:
 Ammonia water
 Potassium Hydroxide
 Distilled water
The samples are divided into four groups:
 Unmodified TiO2
 TiO2 treated with NH4OH:pH = 7 (TiO2–2.5%N) or pH = 8 ( TiO2–8%N)
TiO2 treated with KOH :TiO2–1.5%K (pH = 13),TiO2–2.5%K (pH = 13) and TiO2 10%K (pH = 14),
 TiO2 treated with both NH4OH and KOH. :TiO2–2.5%N/1.5%K(pH =13)
TiO2–2.5%N/2.5%K (pH = 13) and TiO2–2.5%N/10%K (pH = 14),
CO2 adsorption capacity
 In case of KOH treatment the decrease of both the surface area and the mesopore volume was observed. The
treatment introduced significant amounts of KOH which is solid.
 This material can occupy volume of mesopores resulting in the observed decrease of the surface area and pore
 The increase of the average crystallite sizes was observed in this case which can be attributed to the ammonia
 The change in the pores volume was an effect of two factors.
 Washing out of small crystallites resulting in an increase of volume
 blocking of pores volume by solid KOH resulting in a decrease of volume.
 The same reasoning can be applied for the changes in surface area.
CO2 adsorption capacity (contd.)
 In unmodified TiO2, The CapBT and CapTotal values were 0.03 mmol/g and 0.06 mmol/g, respectively having poor
adsorption capacity.
 After treating with NH4OH, the total capacity for TiO2–2.5%N and TiO2–8%N reached 0.10 mmol/g and 0.14 mmol/g,
which improved the adsorption to 67 % and 133%.
 This is due to contribution of the ammonia groups, which had a high affinity towards CO2 due to the acid-base interaction.
 The results of CO2 adsorption on the materials treated with KOH solutions are shown in Fig. 8.
 The CO2 breakthrough time was around 2.5 min which corresponded to the breakthrough capacity of 0.07 mmol/g.
 The CAPtotal was 0.24 mmol/g which increased due to KOH treatment which increased the sorbent capacity to 4 times
than unmodified material.
 The time required to reach the adsorption equilibrium was the longest in case of the sample modified with the most
concentrated KOH (TiO2–10%K ) which was 6 times more than unmodified Tio2.
CO2 adsorption capacity (contd.)
 For all these samples the CO2 breakthrough time was similar to that observed for the
materials modified with 2.5% and 10% KOH solution (4.5 min)
 The time required to reach the equilibrium in case of TiO2 2.5%N/1.5%K and TiO2–
2.5%N/ 2.5%K samples was 18 and 23 min.
 It was shorter than that measured for TiO2–2.5%N/10%K sample (30 min).
 The CapTotal value calculated for the latter material was almost 9 times higher than that
observed in case of unmodified titania.
 A comparison of the CO2 breakthrough capacities obtained for the most efficient sorbents obtained by various
modification is presented.
 The observed differences in the adsorption capacity of the materials can
be caused by various textural parameters and surface chemistry.
 In the case of the materials modified with NH4OH the better
performance corresponded to the increase of the surface area.
 Moreover, the CO2 uptake increased with the decrease of surface area of
the KOH-modified samples.
 These data led to a conclusion that surface chemistry was more
important for CO2 sorption than the surface area.
 Samples treated with KOH were more basic than those modified with
 It was found that the sorption properties of the materials were affected mainly by the surface chemistry which was then
related to the preparation conditions such as the type of modifying agents (NH4OH or KOH) and concentration of
modification solution.
 Modification of TiO2 with KOH allowed to obtain more efficient CO2 sorbents compared to those prepared with
application of ammonia.
 The co-modification of Titania with NH4OH and KOH allowed to increase the total adsorption capacity of TiO2 for 9
times compared to the untreated sample.
 Besides the excellent CO2 adsorption capacity, the TiO2 treated with 2.5% NH4OH and 10% KOH solutions exhibited a
very good stability and regenerability.
Thank You