CrystEngComm Blog

Nanolimes, alcoholic dispersions of colloidal Ca(OH)₂ nanoparticles, are commonly used for the conservation of porous materials such as stone and marble.  However, only the basics of the process they undergo – carbonation to produce CaCO₃ – are understood and this limits their potential use.

A new paper by Rodriguez-Navarro looks at the carbonation process in detail, with the aims of increasing the effectiveness of and understanding any limitations in the use of nanolimes in conservation.

Conservation of materials using nanolimes is typically carried out in humid air at room temperature.  Under these conditions, amorphous calcium carbonate (ACC) initially forms.  This can then transform into the metastable vaterite (up to 35 wt%) and a small amount of aragonite (up to 5%), but only in the presence of alcohol.  These polymorphs partially dissolve and the stable polymorph, calcite, precipitates.  Alternatively, calcite can form directly after dissolution of ACC.

Results of the kinetic studies show that the rate-limiting step in the production of calcite is the amount of unreacted Ca(OH)₂.  Although the formation of metastable states might be considered a limitation to the use of nanolimes in conservation, the fast kinetics of the vaterite to calcite conversion (72 % in 10 days) means that almost the full consolidation potential can be reached within weeks of application and it is only over very short time-scales that the performance might be sub-optimal.

These results may also have implications for the design of new CaCO₃ materials for other applications, using syntheses analogous to the multi-step crystallisation shown in the carbonation of nanolimes in the presence of alcohol.

For more information, read the full paper at:

Amorphous and crystalline calcium carbonate phases during carbonation of nanolimes: implications in heritage conservation

Carlos Rodriguez-Navarro, Kerstin Elert and Radek Ševčík

CrystEngComm, 2016, Advance Article
DOI: 10.1039/C6CE01202G, Paper

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She published a book, ‘Molecules, Medicines and Mischief’, in 2014, on some of the chemicals found in plants and is currently working on a follow-up.

A recent paper published in CrystEngComm details the successful development of BiOBr/WO₃ p–n heterojunctions. These novel photocatalysts display higher activity than the individual components across a range of organic molecule pollutants and remain stable for further cycles.

Semiconducting photocatalysts offer a potentially green way of removing organic pollutants from water. Initial development of these photocatalysts focused on TiO₂, which shows excellent performance for the decomposition of many organic compounds. However, TiO₂ only exhibits this performance under UV light and the development of visible light driven (VLD) photocatalysts is highly desirable. WO₃, an n-type semiconductor, possesses many properties needed for a good VLD, but encounters problems related to the recombination of charge carriers.

It is known that the creation of p-n heterojunctions can enhance performance. Enter bismuth oxyhalides, p-type semiconductors which exhibit excellent performance under both UV and visible light. BiOBr in particular, has good chemical stability, acts against a wide range of pollutants, and has never been combined with WO₃ before.

The heterojunctions were prepared by solvothermally treating a solution of WO₃, Bi(NO₃)₃ and CTAB. Three different molar ratios were prepared (1/0.5, 1/1 and 1/2) creating flower-like structures. The individual components were also prepared for comparative measurements. Photocatalytic activity was measured by the decomposition of three organic compounds, rhodamine B, methyl orange and para-chlorophenol. The 1/1 compound showed the greatest removal efficiency across all the mock pollutants with all heterojunction ratios performing better than the individual components and a mixture of the two with the same weight of components. The authors explain the excellent performance of BiOBr/WO₃ is due to two reasons; firstly the flower-like superstructures of the material with their many pores and channels increase the absorption of small molecules and secondly the nature of the p-n heterojunction allows for efficient charge collection and separation.

The authors conclude the 1/1 compound is the best potential visible light driven photocatalyst with efficient performance and good stability for water environmental purification.

Read the full article here:

Synthesis of BiOBr/WO₃ p–n heterojunctions with enhanced visible light photocatalytic activity
Junlei Zhang, Lisha Zhang, Xiaofeng Shen, Pengfei Xu and Jianshe Liu
CrystEngComm, 2016,18, 3856-3865, DOI: 10.1039/C6CE00824K

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	Josh Campbell is a PhD student, currently at the University of Southampton, UK studying crystal structure prediction of organic semiconductors. He received his BSc from the University of Bradford.

The most downloaded articles for the months of October, November and December 2015 were:

Nanocrystal engineering of noble metals and metal chalcogenides: controlling the morphology, composition and crystallinity
Lakshminarayana Polavarapu, Stefanos Mourdikoudis, Isabel Pastoriza-Santos and  Jorge Pérez-Juste
CrystEngComm, 2015, 17, 3727-3762
DOI: 10.1039/C5CE00112A

Fundamental growth principles of colloidal metal nanoparticles – a new perspective
Jörg Polte
CrystEngComm, 2015, 17, 6809-6830
DOI: 10.1039/C5CE01014D

Layered organic–inorganic hybrid perovskites: structure, optical properties, film preparation, patterning and templating engineering
Ziyong Cheng and Jun Lin*
CrystEngComm, 2010, 12, 2646-2662
DOI: 10.1039/C001929A

A comprehensive review on synthesis methods for transition-metal oxide nanostructures
Ting Guo, Ming-Shui Yao, Yuan-Hua Lin* and Ce-Wen Nan
CrystEngComm, 2015, 17, 3551-3585
DOI: 10.1039/C5CE00034C

Bulk crystal growth of hybrid perovskite material CH₃NH₃PbI₃
Yangyang Dang, Yang Liu, Youxuan Sun, Dongsheng Yuan, Xiaolong Liu, Weiqun Lu, Guangfeng Liu, Haibing Xia* and Xutang Tao*
CrystEngComm, 2015, 17, 665-670
DOI: 10.1039/C4CE02106A

How to print a crystal structure model in 3D
Teng-Hao Chen,* Semin Lee, Amar H. Flood and Ognjen Š. Miljanić
CrystEngComm, 2014, 16, 5488-5493
DOI: 10.1039/C4CE00371C

Rational design of metal–organic frameworks with anticipated porosities and functionalities
Muwei Zhang, Mathieu Bosch, Thomas Gentle III and Hong-Cai Zhou*
CrystEngComm, 2014, 16, 4069-4083
DOI: 10.1039/C4CE00321G

Transition metal carboxylate coordination polymers with amide-bridged polypyridine co-ligands: assemblies and properties
Ju-Wen Zhang, Xiao-Min Kan, Xiao-Li Li, Jian Luan and Xiu-Li Wang*
CrystEngComm, 2015, 17, 3887-3907
DOI: 10.1039/C4CE02531H

Metal–organic frameworks as heterogeneous photocatalysts: advantages and challenges
M. A. Nasalevich, M. van der Veen, F. Kapteijn and J. Gascon*
CrystEngComm, 2014, 16, 4919-4926
DOI: 10.1039/C4CE00032C

Tuning of the crystal engineering and photoelectrochemical properties of crystalline tungsten oxide for optoelectronic device applications
Jin You Zheng, Zeeshan Haider, Thanh Khue Van, Amol Uttam Pawar, Myung Jong Kang, Chang Woo Kim and Young Soo Kang*
CrystEngComm, 2015, 17, 6070-6093
DOI: 10.1039/C5CE00900F

The structure-directing properties of 2,4,6-trimethylpyridine (TMP) for the formation of colloidal C₆₀-fullerene are revealed in a new paper by Penterman and Liddell Watson.

C₆₀-fullerenes can support singlet excited states that recombine to produce a red photoluminescence and also have a high refractive index and transparency.  As such, they have a potential use in colloid-based photonic crystals.  Fullerene microcrystals are typically prepared in a solvent-antisolvent system, where the antisolvent promotes nucleation.  The solvent-antisolvent ratio, concentration of fullerene, temperature and mixing conditions can be varied to produce particles with different morphologies. However, there are not many compatible solvent-antisolvent combinations, limiting the nature of the particles that can form.

In this paper, the effect of adding TMP to the tetralin or mesitylene:2-propanol solvent-antisolvent system, is investigated.  When the solvent is tetralin, TMP plays a dominant role in determining the colloid morphology, monodispersity and crystal structure (an SEM of one fullerene solvate produced is shown below).  In the mesitylene  system, the crystals have well-defined faceting, higher aspect ratios and improved packing efficiency.

The microcrystals show a reduced fluorescence quantum yield and lifetime, which is thought to be a result of greater fullerene packing efficiency. This is enhanced as the polar TMP additive acts as a blocking agent, adsorbing at the solid–liquid interface and slowing the kinetic rates of growth on certain crystallographic planes. The nucleation period is also shortened, supporting monodispersity.

The use of structure-directing agents could allow the production of fullerene microcrystals with diverse internal crystal structures and external forms.  This may allow the development of fullerenes tuned to possess specific properties, including suitability for use as active building blocks for photonic crystals.  The authors are continuing to explore the potential of this application.

For more details, see the full paper at:

CrystEngComm, 2016
DOI: 10.1039/C5CE02122G

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Gwenda Kyd has a PhD in metallocarborane chemistry from the University of Edinburgh. Other research work includes the spectroscopic study of the structure of glasses and organometallic electron-transfer reactions and the preparation of new inorganic phosphors. She has recently published a book on chemicals from plants.