L.E. Trujillo and F.J. Willars Rodr&#237;guez thank CONACYT for their scholarships. E.A. Chavez-Urbiola thanks CONACYT for the &#34;Catedras CONACYT&#34; program. Authors also acknowledge the technical assistance of C.A. Avila Herrera, M. A. Hern&#225;ndez Landaverde, J.E. Urbina Alv&#225;rez, and A. Jim&#233;nez Nieto.

CAUTION: The chemicals used in this protocol are toxic and carcinogenic; thus, the safety recommendations and procedures must be followed carefully. Wear proper protective equipment and consult any relevant materials safety data sheet (MSDS).
1. Synthesis of Bis(thiourea) Cadmium Chloride
<ol>
	<li>Preparation of the precursor solution
	<ol>
		<li>Pour 500 mL of deionized water into a 1 L beaker with constant agitation; add 0.3 mL of hydrochloric acid at a 36.5% concentration, making sure that the pH of the solution is as close as possible to 3, using a pH meter. 
		CAUTION: To avoid any health effects, performing this action inside a fume hood is highly recommended.</li>
		<li>Pour 50 mL of the precursor solution prepared as indicated in step 1.1.1 into each of two 100 mL beakers (hereafter, these beakers will be named A and B). 
		NOTE: Two experiments (A and B, dependent on the beaker used) are carried out simultaneously. Only experiment B will be exposed to UV light.</li>
	</ol>
	</li>
	<li>Weigh 2.29 g of CdCl2 for each beaker (A and B). 
	CAUTION: Perform this action inside the fume hood as the material used is identified as hazardous. Cadmium is highly toxic and identified as carcinogenic when inhaled; it must be handled carefully.</li>
	<li>Weigh 1.33 g of CS(NH2)2 for each beaker (A and B). 
	CAUTION: Perform this action inside the fume hood as the material used is dangerously unhealthy. Thiourea is highly toxic when inhaled and must be handled carefully.</li>
	<li>Add 2.29 g of CdCl2 and 1.33 g of CS(NH2)2 to each beaker (A and B) containing 50 mL of the precursor solution.</li>
</ol>
2. Comparative Synthesis of Bis(thiourea) Cadmium Chloride
<ol>
	<li>Experimental arrangement without UV light (A).
	<ol>
		<li>Place the beaker (A) on the stirring hot plate and heat it up to 343 K. Set the plate on a moderate stirring speed. 
		CAUTION: Perform this action inside the fume hood.</li>
		<li>Keep the solution in the beaker (A) moderately stirring for 2 h on the plate at 343 K.</li>
	</ol>
	</li>
	<li>Experimental arrangement with UV light (B).
	<ol>
		<li>Place the beaker B on the plate and heat it up to 343 K. Set the stirring speed on a moderate level and switch on the UV light source. 
		NOTE: The experimental arrangement is shown in Figure 1. 
		CAUTION: Perform this action inside the fume hood.</li>
		<li>Keep the temperature and stirring conditions as described in step 2.2.1 for 2 h.</li>
	</ol>
	</li>
</ol>
3. Obtaining Bis(thiourea) Cadmium Chloride Crystals
<ol>
	<li>Mount 2 glass funnels with filter paper (No. 40, &#216; = 125 mm), each one over a 100 mL volumetric flask, for A and B. To avoid the crystal formation at this stage; do not let the solution cool before filtering it.</li>
	<li>Filter the solutions A and B through the paper, each into their own 100 mL flask. 
	CAUTION: Perform this action inside the fume hood.</li>
	<li>Let both solutions inside the volumetric flasks cool to room temperature. 
	NOTE: The crystals begin to grow in the first minutes inside the volumetric flasks.</li>
	<li>Prepare the filtering assembly again (step 3.1) with a new filter paper.</li>
	<li>Filter the solutions with the crystals through the filter paper into separate volumetric flasks. 
	CAUTION: Perform this action inside the fume hood.</li>
	<li>Transfer the crystals on the filter paper to the respective watch glass. 
	NOTE: At this point, there are 2 watch glasses, 1 for A and 1 for B.</li>
	<li>Confirm the presence of bis(thiourea) cadmium chloride crystals by powder X-ray diffraction (XRD) and Raman spectroscopy, as reported in Trujillo et al.12.</li>
</ol>
4. Calcination of the Crystals to Obtain CdS
<ol>
	<li>Place the crystals obtained in step 3.7 into 2 different crucibles, 1 for A and 1 for B.</li>
	<li>Preheat an electric laboratory furnace and stabilize its temperature at 773 K or higher.</li>
	<li>Place the crucibles of step 4.1 inside the preheated furnace. 
	CAUTION: The released vapors during calcination are toxic. Make sure that the furnace is in a fume hood due to the toxic fumes that it will be exhausted.</li>
	<li>Let the material stand inside the furnace for 1 h at 773 K. Then, turn off the furnace and let it cool to room temperature. After that, remove the crucibles from the oven.</li>
</ol>

<ol>
	<li>Venkataramanan, V., Maheswaran, S., Sherwood, J. N., Bhat, H. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Crystal+growth+and+physical+characterization+of+the+semiorganic+bis(thiourea)+cadmium+chloride.">Crystal growth and physical characterization of the semiorganic bis(thiourea) cadmium chloride.</a> Journal of Crystal Growth. 179 (3-4), 605-610 (1997).</li><li>Ushasree, P. M., Muralidharan, R., Jayavel, R., Ramasamy, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+of+bis(thiourea)+cadmium+chloride+single+crystals+a+potential+NLO+material+of+organometallic+complex.">Growth of bis(thiourea) cadmium chloride single crystals a potential NLO material of organometallic complex.</a> Journal of Crystal Growth. 218 (2-4), 365-371 (2000).</li><li>Ushasree, P. M., Jayavel, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+and+micromorphology+of+as-grown+and+etched+bis(thiourea)+cadmium+chloride+(BTCC)+single+crystals.">Growth and micromorphology of as-grown and etched bis(thiourea) cadmium chloride (BTCC) single crystals.</a> Optical Materials. 21 (1-3), 569-604 (2002).</li><li>Pawar, S. M., Pawar, B. S., Kim, J. H., Joo, O., Lokhande, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+status+of+chemical+bath+deposited+metal+chalcogenide+and+metal+oxide+thin+films.">Recent status of chemical bath deposited metal chalcogenide and metal oxide thin films.</a> Current Applied Physics. 11 (2), 117-161 (2011).</li><li>Suriakarthick, R., Kumar, V. N., Shyju, T. S., Gopalakrishnan, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Investigation+on+post+annealed+copper+sulfide+thin+films+from+photochemical+deposition+technique.">Investigation on post annealed copper sulfide thin films from photochemical deposition technique.</a> Materials Science in Semiconductor Processing. 26 (1), 155-161 (2014).</li><li>Podder, J., Kobayashi, R., Ichimura, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photochemical+deposition+of+Cu+x+S+thin+films+from+aqueous+solutions.">Photochemical deposition of Cu x S thin films from aqueous solutions.</a> Thin Solid Films. 472 (1-2), 71-75 (2005).</li><li>Gunasekaran, M., Gopalakrishnan, R., Ramasamy, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deposition+of+ZnS+thin+films+by+photochemical+deposition+technique.">Deposition of ZnS thin films by photochemical deposition technique.</a> Materials Letters. 58 (1-2), 67-70 (2004).</li><li>Ichimura, M., Goto, F., Ono, Y., Arai, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deposition+of+CdS+and+ZnS+from+aqueous+solutions+by+a+new+photochemical+technique.">Deposition of CdS and ZnS from aqueous solutions by a new photochemical technique.</a> Journal of Crystal Growth. 198 (1), 308-312 (1999).</li><li>Kumaresan, R., Ichimura, M., Sato, N., Ramasamy, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+novel+photochemical+deposition+technique+for+the+deposition+of+indium+sulfide.">Application of novel photochemical deposition technique for the deposition of indium sulfide.</a> Materials Science Engineering: B. 96 (1), 37-42 (2002).</li><li>Rama, G., Jeevanandam, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+of+different+morphologies+of+CdS+nanoparticles+by+thermal+decomposition+of+bis(thiourea)cadmium+chloride+in+various+solvents.">Evolution of different morphologies of CdS nanoparticles by thermal decomposition of bis(thiourea)cadmium chloride in various solvents.</a> Journal of Nanoparticle Research. 17 (1), 1-13 (2015).</li><li>Pabitha, G., Dhanasekaran, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+and+characterization+of+a+nonlinear+optical+crystal+-+bis+thiourea+cadmium+chloride.">Growth and characterization of a nonlinear optical crystal - bis thiourea cadmium chloride.</a> International Journal of Innovative Research in Science, Engineering and Technology. 4 (1), 34-38 (2015).</li><li>Trujillo, L. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Di-thiourea+cadmium+chloride+crystals+synthesis+under+UV+radiation+influence.">Di-thiourea cadmium chloride crystals synthesis under UV radiation influence.</a> Journal of Crystal Growth. 478 (1), 140-145 (2017).</li><li>Elilarassi, R., Maheshwari, S., Chandrasekaran, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structural+and+optical+characterization+of+CdS+nanoparticles+synthesized+using+a+simple+chemical+reaction+route.">Structural and optical characterization of CdS nanoparticles synthesized using a simple chemical reaction route.</a> Optoelectronics and Advanced Materials - Rapid Communications. 4 (3), 309-312 (2010).</li><li>Selvasekarapandian, S., Vivekanandan, K., Kolandaivel, P., Gundurao, T. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vibrational+Studies+of+Bis(thiourea)+Cadmium+Chloride+and+Tris(thiourea)+Zinc+Sulphate+Semiorganic+Non-linear+Optical+Crystals.">Vibrational Studies of Bis(thiourea) Cadmium Chloride and Tris(thiourea) Zinc Sulphate Semiorganic Non-linear Optical Crystals.</a> Crystal Research &amp; Technology. 32 (2), 299-309 (1997).</li></ol>

The authors have nothing to disclose.

The discussion presented in this section focuses only on the protocol and not on the results already shown in the representative results.
One of the most critical parts of the protocol is the preparation of the precursor solution. It is fundamental to maintain an acidic pH to avoid the Cd(OH)2 formation. If the pH is not acidic, it leads to the direct formation of CdS due to the thiourea dissociation and the Cd(OH)2 formation. 
The second most important step is step ...

An important area of research is single crystals; their growth is aimed at different applications. These can be used as non-linear optical materials applied in the areas of laser technology, in the field of optoelectronics, and for the storage of information1, which provides an area of opportunity for their investigation. Bis(thiourea) cadmium chloride is a metal-organic material and can be synthesized from two precursors, thiourea and cadmium chloride, obeying the following chemical formula: 2CS(NH2)2 + CdCl2 CdCl2-[CS(NH2)2]2. This metal-organic material has been prepared under different reaction conditions, such as temperature and pH, but never with the assistance of ultraviolet (UV) light.
The influence of pH on the structure of the crystal has been reported; at a pH &#60; 6, it is possible to obtain the formation of monocrystals. These, in turn, are modified depending on the pH range. At an interval of 6 to 4, it is possible to obtain hexagonal structures, for if pH is &#60; 4, an orthorhombic crystalline structure is obtained2. The ion dissociation is promoted by the acidic pH Cd2+ and Cl- since it prevents cadmium hydroxide formation [Cd(OH)2]. This stabilizes the cadmium: a cadmium atom joins with two sulfur-free radicals and two chlorines.
Here, the synthesis is carried out using the chemical bath deposition technique (CBD), controlling the different conditions that intervene at the time of the chemical reaction3. In CBD, the factors that control the chemical reaction are the following: the solution temperature, the precursor ions, the solution pH, the number of reagents, and the agitation speed, to name a few. On the other hand, the compared technique used here is called photochemical bath deposition (PCBD) because it uses UV light assistance. There have been reports in which UV light assistance has been used to synthesize films of CuSx4,5, ZnS6, CdS7, and InS8, among others. Ichimura and Gunasekaran9 present in their work that sulfate solutions have an absorption edge close to 300 nm. Due to this absorption range, ultraviolet radiation is applied, which results in a similar emission range to that of the absorbed solutions.
Another property of bis(thiourea) cadmium chloride is its degradation when heated. It exhibits an initial decomposition at temperatures of 512 K and above, forming cadmium sulfide (CdS). The degradation reaction is as follows: [Cd(CS[NH2])2]Cl2 &#8594; &#916; CdS + HNCS + NH3 + NH4SCN. This degradation generates thiocyanuric acid and various thiocyanates10,11. Also, in the research group, some effects caused by the UV radiation were studied12. Last, in this work, a comparative synthesis procedure for bis(thiourea) cadmium chloride crystals is described, as well as the effects of UV light.

<table><tbody><tr><td>&lt;strong&gt;Reagents&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Cadmium chloride Anh. ACS, 99.4 %</td><td>Fermont</td><td>PQ24291</td><td>Highly toxic</td></tr><tr><td>Thiourea technical grade, 99.9 %</td><td>Reasol</td><td>R5913</td><td>Toxic</td></tr><tr><td>Hydrochloric acid, 36.5 &amp;ndash; 38.0 %</td><td>J.T.Baker</td><td>MFCD00011324</td><td>Highly corrosive liquid</td></tr><tr><td>&lt;strong&gt;Material&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Filter paper</td><td>Whatman</td><td>1440 125</td><td>40, Ashless, Circles, 125 mm</td></tr><tr><td>Beaker</td><td>Kimax</td><td>1400</td><td>100 mL</td></tr><tr><td>Volumetric Flask</td><td>Kimax</td><td>28012-100</td><td>Class A 100 mL</td></tr><tr><td>Glass Funnel</td><td>Kimax</td><td>28980-150</td><td>Addition Funnel, Long Stem, 60&amp;deg; Angle, Wide Top. Type I, Class B.</td></tr><tr><td>Watch glasses</td><td>Pyrex</td><td>9985-150</td><td>Corning, 150&amp;nbsp;mm</td></tr><tr><td>Crucibles</td><td>Fisherbrand</td><td>FB-965-D</td><td>High-Form Porcelain</td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Furnace</td><td>Briteg Instrumentos Cientificos S.A. de C.V.</td><td>1010</td><td></td></tr><tr><td>Fume Hood</td><td>Fisher Alders, S.A. de C.V.</td><td>F1124</td><td></td></tr><tr><td>Light surce</td><td>Philips</td><td>PL-S 9W UV-A/2P 1CT/6X 10 CC</td><td></td></tr><tr><td>pH meter</td><td>OAKTON</td><td>WD-35419-10</td><td></td></tr><tr><td>Hotplate whit magnetic stirrer</td><td>Cole-Parmer</td><td>JZ-04660-75</td><td></td></tr></tbody></table>

the effect of ultraviolet radiation on the chemical bath deposition of bis(thiourea) cadmium chloride crystals and the subsequent cds obtention

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of 367 nm using the chemical bath deposition technique are studied comparatively. Two experiments are performed to make a comparison: one without UV light and the other with the aid of UV light. Both experiments are performed under equal conditions, at a temperature of 343 K and with a pH of 3.2. The precursors used are cadmium chloride (CdCl2) and thiourea [CS(NH2)2], which are dissolved in 50 mL of deionized water with an acidic pH. In this experiment, the interaction of electromagnetic radiation is sought at the moment the chemical reaction is carried out. The results demonstrate the existence of an interaction between the crystals and the UV light; the UV light assistance causes crystal growths in an acicular shape. Also, the final product obtained is cadmium sulfide and shows no evident difference when synthesized with or without the use of UV light.

The UV-Vis diffusion&#39;s reflectance absorption spectra in both precursor solutions, A and B, show the existence of a bis(thiourea) cadmium chloride complex&#8212;CdCl2-(CS(NH2)2)2. This is evidenced by a broad absorption band within the range of 250 - 500 nm in Figure 2c. In turn, Figure 2c is the combination of the main absorption bands of the isolated CdCl2 and CS(NH<sub...

Watch this Scientific Journal Video about The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bisthiourea Cadmium Chloride Crystals and the Subsequent CdS Obtention at JoVE.com

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bisthiourea Cadmium Chloride Crystals and the Subsequent CdS Obtention

This article presents a protocol for the synthesis of bis(thiourea) cadmium chloride crystals by chemical bath deposition. Two experiments are described: one aided by ultraviolet light compared to one without ultraviolet light.

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bis(thiourea) Cadmium Chloride Crystals and the Subsequent CdS Obtention

In this work, the effects on the preparation of bis(thiourea) cadmium chloride crystals when illuminated with ultraviolet (UV) light at a wavelength of ...

the-effect-ultraviolet-radiation-on-chemical-bath-deposition-bis

Research

JoVE Journal

Chemistry

7.4K Views.  Universidad Autónoma del Estado de Hidalgo. Dit artikel presenteert een protocol voor de synthese van bis(thiourea) cadmium chloride kristallen door chemische Bad afzetting. Twee experimenten worden beschreven: een geholpen door ultraviolet licht in vergelijking met zonder ultraviolet licht.

Video: The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bisthiourea Cadmium Chloride Crystals and the Subsequent CdS Obtention

Compact Quantum Dots for Single-molecule Imaging

Single-molecule imaging is an important tool for understanding the mechanisms of biomolecular function and for visualizing the spatial and temporal heterogeneity of molecular behaviors that underlie cellular biology 1-4. To image an individual molecule of interest, it is typically conjugated to a fluorescent tag (dye, protein, bead, or quantum dot) and observed with epifluorescence or total internal reflection fluorescence (TIRF) microscopy. While dyes and fluorescent proteins have been the mainstay of fluorescence imaging for decades, their fluorescence is unstable under high photon fluxes necessary to observe individual molecules, yielding only a few seconds of observation before complete loss of signal. Latex beads and dye-labeled beads provide improved signal stability but at the expense of drastically larger hydrodynamic size, which can deleteriously alter the diffusion and behavior of the molecule under study.
Quantum dots (QDs) offer a balance between these two problematic regimes. These nanoparticles are composed of semiconductor materials and can be engineered with a hydrodynamically compact size with exceptional resistance to photodegradation 5. Thus in recent years QDs have been instrumental in enabling long-term observation of complex macromolecular behavior on the single molecule level. However these particles have still been found to exhibit impaired diffusion in crowded molecular environments such as the cellular cytoplasm and the neuronal synaptic cleft, where their sizes are still too large 4,6,7.
Recently we have engineered the cores and surface coatings of QDs for minimized hydrodynamic size, while balancing offsets to colloidal stability, photostability, brightness, and nonspecific binding that have hindered the utility of compact QDs in the past 8,9. The goal of this article is to demonstrate the synthesis, modification, and characterization of these optimized nanocrystals, composed of an alloyed HgxCd1-xSe core coated with an insulating CdyZn1-yS shell, further coated with a multidentate polymer ligand modified with short polyethylene glycol (PEG) chains (Figure 1). Compared with conventional CdSe nanocrystals, HgxCd1-xSe alloys offer greater quantum yields of fluorescence, fluorescence at red and near-infrared wavelengths for enhanced signal-to-noise in cells, and excitation at non-cytotoxic visible wavelengths. Multidentate polymer coatings bind to the nanocrystal surface in a closed and flat conformation to minimize hydrodynamic size, and PEG neutralizes the surface charge to minimize nonspecific binding to cells and biomolecules. The end result is a brightly fluorescent nanocrystal with emission between 550-800 nm and a total hydrodynamic size near 12 nm. This is in the same size range as many soluble globular proteins in cells, and substantially smaller than conventional PEGylated QDs (25-35 nm).

We describe the preparation of colloidal quantum dots with minimized hydrodynamic size for single-molecule fluorescence imaging. Compared to conventional quantum dots, these nanoparticles are similar in size to globular proteins and are optimized for single-molecule brightness, stability against photodegradation, and resistance to nonspecific binding to proteins and cells.

Single-molecule imaging is an important tool for  understanding the mechanisms of biomolecular function and for visualizing the  spatial and temporal ...

Engineering

Harvesting Solar Energy by Means of Charge-Separating Nanocrystals and Their Solids

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials offering a superior control over the spatial distribution of charge carriers across material interfaces. As this study demonstrates, a combination of donor-acceptor nanocrystal (NC) domains in a single nanoparticle can lead to the realization of efficient photocatalytic1-5 materials, while a layered assembly of donor- and acceptor-like nanocrystals films gives rise to photovoltaic materials.
Initially the paper focuses on the synthesis of composite inorganic nanocrystals, comprising linearly stacked ZnSe, CdS, and Pt domains, which jointly promote photoinduced charge separation. These structures are used in aqueous solutions for the photocatalysis of water under solar radiation, resulting in the production of H2 gas. To enhance the photoinduced separation of charges, a nanorod morphology with a linear gradient originating from an intrinsic electric field is used5. The inter-domain energetics are then optimized to drive photogenerated electrons toward the Pt catalytic site while expelling the holes to the surface of ZnSe domains for sacrificial regeneration (via methanol). Here we show that the only efficient way to produce hydrogen is to use electron-donating ligands to passivate the surface states by tuning the energy level alignment at the semiconductor-ligand interface. Stable and efficient reduction of water is allowed by these ligands due to the fact that they fill vacancies in the valence band of the semiconductor domain, preventing energetic holes from degrading it. Specifically, we show that the energy of the hole is transferred to the ligand moiety, leaving the semiconductor domain functional. This enables us to return the entire nanocrystal-ligand system to a functional state, when the ligands are degraded, by simply adding fresh ligands to the system4.
To promote a photovoltaic charge separation, we use a composite two-layer solid of PbS and TiO2 films. In this configuration, photoinduced electrons are injected into TiO2 and are subsequently picked up by an FTO electrode, while holes are channeled to a Au electrode via PbS layer6. To develop the latter we introduce a Semiconductor Matrix Encapsulated Nanocrystal Arrays (SMENA) strategy, which allows bonding PbS NCs into the surrounding matrix of CdS semiconductor. As a result, fabricated solids exhibit excellent thermal stability, attributed to the heteroepitaxial structure of nanocrystal-matrix interfaces, and show compelling light-harvesting performance in prototype solar cells7.

A general strategy for the development of charge-separating semiconductor nanocrystal composites deployable for solar energy production is presented. We show that assembly of donor-acceptor nanocrystal domains in a single nanoparticle geometry gives rise to a photocatalytic function, while bulk-heterojunctions of donor-acceptor nanocrystal films can be used for photovoltaic energy conversion.

Conjoining different semiconductor materials in a single nano-composite provides synthetic means for the development of novel optoelectronic materials ...

Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded synthesis strategy is used in which spherical seeds of CdSe are prepared first using a hot-injection technique. By controlling the crystal structure of the seed to be either wurtzite or zinc-blende, the subsequent hot-injection growth of CdS off of the seed results in either a rod-shaped or tetrapod-shaped nanocrystal, respectively. The phase and morphology of the synthesized nanocrystals are confirmed using X-ray diffraction and transmission electron microscopy, demonstrating that the nanocrystals are phase-pure and have a consistent morphology. The extinction coefficient and quantum yield of the synthesized nanocrystals are calculated using UV-Vis absorption spectroscopy and photoluminescence spectroscopy. The rods and tetrapods exhibit extinction coefficients and quantum yields that are higher than that of the bare seeds. This synthesis demonstrates the precise arrangement of materials that can be achieved at the nanoscale by using a seeded synthetic approach.

A protocol for the seeded synthesis of rod-shaped and tetrapod-shaped multicomponent nanostructures consisting of CdS and CdSe is presented.

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Facet-to-facet Linking of Shape-anisotropic Colloidal Cadmium Chalcogenide Nanostructures

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be covalently and site-specifically linked via their end facets, resulting in polymer-like linear or branched chains. The linking procedure begins with a cation-exchange process in which the end facets of the cadmium chalcogenide NCs are first converted to silver chalcogenide. This is followed by the selective removal of ligands at their surface. This results in cadmium chalcogenide NCs with highly reactive silver chalcogenide end facets that spontaneously fuse upon contact with each other, thereby establishing an interparticle facet-to-facet attachment. Through the judicious choice of precursor concentrations, an extensive network of linked NCs can be produced. Structural characterization of the linked NCs is carried out via low- and high-resolution transmission electron microscopy (TEM), as well as energy-dispersive X-ray spectroscopy, which confirm the presence of silver chalcogenide domains between chains of cadmium chalcogenide NCs.

A protocol detailing how shape-anisotropic colloidal cadmium chalcogenide nanocrystals can be covalently linked via their end facets is presented here.

Here, we describe a protocol that allows for shape-anisotropic cadmium chalcogenide nanocrystals (NCs), such as nanorods (NRs) and tetrapods (TPs), to be ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Key Factors Affecting the Performance of Sb2S3-sensitized Solar Cells During an Sb2S3 Deposition via SbCl3-thiourea Complex Solution-processing

Sb2S3 is considered as one of the emerging light absorbers that can be applied to next-generation solar cells because of its unique optical and electrical properties. Recently, we demonstrated its potential as next-generation solar cells by achieving a high photovoltaic efficiency of &#62; 6% in Sb2S3-sensitized solar cells using a simple thiourea (TU)-based complex solution method. Here, we describe the key experimental procedures for the deposition of Sb2S3 on a mesoporous TiO2 (mp-TiO2) layer using a SbCl3-TU complex solution in the fabrication of solar cells. First, the SbCl3-TU solution is synthesized by dissolving SbCl3 and TU in N,N-dimethylformamide at different molar ratios of SbCl3:TU. Then, the solution is deposited on as-prepared substrates consisting of mp-TiO2/TiO2-blocking layer/F-doped SnO2 glass by spin coating. Finally, to form crystalline Sb2S3, the samples are annealed in an N2-filled glove box at 300 &#176;C. The effects of the experimental parameters on the photovoltaic device performance are also discussed.

Key Factors Affecting the Performance of Sb2S3-sensitized Solar Cells During an Sb2S3 Deposition via SbCl3-thiourea Complex Solution-processing

This work provides a detailed experimental procedure for the deposition of Sb2S3 on a mesoporous TiO2 layer using a SbCl3-thiourea complex solution for applications in Sb2S3-sensitized solar cells. This article also determines key factors governing the deposition process.

Sb2S3 is considered as one of the emerging light absorbers that can be applied to next-generation solar cells because of its unique optical and electrical ...

A Facile Synthetic Method to Obtain Bismuth Oxyiodide Microspheres Highly Functional for the Photocatalytic Processes of Water Depuration

Bismuth oxyhalide (BiOI) is a promising material for sunlight-driven-environmental photocatalysis. Given that the physical structure of this kind of materials is highly related to its photocatalytic performance, it is necessary to standardize the synthetic methods in order to obtain the most functional architectures and, thus, the highest photocatalytic efficiency. Here, we report a reliable route to obtain BiOI microspheres via the solvothermal process, using Bi(NO3)3 and potassium iodide (KI) as precursors, and ethylene glycol as a template. The synthesis is standardized in a 150 mL autoclave, at 126 &#176;C for 18 h. This results in 2-3 &#181;m-sized mesoporous microspheres, with a relevant specific surface area (61.3 m2/g). Shortening the reaction times in the synthesis results in amorphous structures, while higher temperatures lead to a slight increase in the porosity of the microspheres, with no effect in the photocatalytic performance. The materials are photo-active under UV-A/visible light irradiation for the degradation of the antibiotic ciprofloxacin in water. This method has demonstrated to be effective in interlaboratory tests, obtaining similar BiOI microspheres in Mexican and Chilean research groups.

This article describes a synthetic method to obtain bismuth oxyiodide microspheres, which are highly functional to perform the photocatalytic removal of organic pollutants, such as ciprofloxacin, in water under UV-A/visible light irradiation.

Bismuth oxyhalide (BiOI) is a promising material for sunlight-driven-environmental photocatalysis. Given that the physical structure of this kind of ...

Fabrication of Robust Nanoscale Contact between a Silver Nanowire Electrode and CdS Buffer Layer in Cu(In,Ga)Se2 Thin-film Solar Cells

Silver nanowire transparent electrodes have been employed as window layers for Cu(In,Ga)Se2 thin-film solar cells. Bare silver nanowire electrodes normally result in very poor cell performance. Embedding or sandwiching silver nanowires using moderately conductive transparent materials, such as indium tin oxide or zinc oxide, can improve cell performance. However, the solution-processed matrix layers can cause a significant number of interfacial defects between transparent electrodes and the CdS buffer, which can eventually result in low cell performance. This manuscript describes how to fabricate robust electrical contact between a silver nanowire electrode and the underlying CdS buffer layer in a Cu(In,Ga)Se2 solar cell, enabling high cell performance using matrix-free silver nanowire transparent electrodes. The matrix-free silver nanowire electrode fabricated by our method proves that the charge-carrier collection capability of silver nanowire electrode-based cells is as good as that of standard cells with sputtered ZnO:Al/i-ZnO as long as the silver nanowires and CdS have high-quality electrical contact. The high-quality electrical contact was achieved by depositing an additional CdS layer as thin as 10 nm onto the silver nanowire surface.

Fabrication of Robust Nanoscale Contact between a Silver Nanowire Electrode and CdS Buffer Layer in CuIn,GaSe2 Thin-film Solar Cells

In this protocol, we describe the detailed experimental procedure for the fabrication of a robust nanoscale contact between a silver nanowire network and CdS buffer layer in a CIGS thin-film solar cell.

Silver nanowire transparent electrodes have been employed as window layers for Cu(In,Ga)Se2 thin-film solar cells. Bare silver nanowire electrodes ...

Close-Space Sublimation-Deposited Ultra-Thin CdSeTe/CdTe Solar Cells for Enhanced Short-Circuit Current Density and Photoluminescence

Developments in photovoltaic device architectures are necessary to make solar energy a cost-effective and reliable source of renewable energy amidst growing global energy demands and climate change. Thin film CdTe technology has demonstrated cost-competitiveness and increasing efficiencies due partially to rapid fabrication times, minimal material usage, and introduction of a CdSeTe alloy into a ~3 &#956;m absorber layer. This work presents the close-space sublimation fabrication of thin, 1.5 &#181;m CdSeTe/CdTe bilayer devices using an automated in-line vacuum deposition system. The thin bilayer structure and fabrication technique minimize deposition time, increase device efficiency, and facilitate future thin absorber-based device architecture development. Three fabrication parameters appear to be the most impactful for optimizing thin CdSeTe/CdTe absorber devices: substrate preheat temperature, CdSeTe:CdTe thickness ratio, and CdCl2 passivation. For proper sublimation of the CdSeTe, the substrate temperature prior to deposition must be ~540 &#176;C (higher than that for CdTe) as controlled by dwell time in a preheat source. Variation in the CdSeTe:CdTe thickness ratio reveals a strong dependence of device performance on this ratio. The optimal absorber thicknesses are 0.5 &#956;m CdSeTe/1.0 &#956;m CdTe, and non-optimized thickness ratios reduce efficiency through back-barrier effects. Thin absorbers are sensitive to CdCl2 passivation variation; a much less aggressive CdCl2 treatment (compared to thicker absorbers) regarding both temperature and time yields optimal device performance. With optimized fabrication conditions, CdSeTe/CdTe increases device short-circuit current density and photoluminescence intensity compared to single-absorber CdTe. Additionally, an in-line close-space sublimation vacuum deposition system offers material and time reduction, scalability, and attainability of future ultra-thin absorber architectures.

This work describes the complete fabrication process of thin absorber cadmium selenium telluride/cadmium telluride photovoltaic devices for enhanced efficiency. The process utilizes an automated in-line vacuum system for close-space sublimation deposition that is scalable, from fabrication of small area research devices as well as large-scale modules.

Developments in photovoltaic device architectures are necessary to make solar energy a cost-effective and reliable source of renewable energy amidst ...

The Effect of Ultraviolet Radiation on the Chemical Bath Deposition of Bis(thiourea) Cadmium Chloride Crystals and the Subsequent CdS Obtention

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