Diffraction

25 Jun 2011
Evaluation Methods: 

Evaluation for the experiment is done through a worksheet-style lab report on which students report their results and answer several questions to probe their understanding of nanoparticle synthesis and powder diffraction.

Evaluation Results: 

I have piloted this experiment four times with a total of 120 students. Every partnership has successfully synthesized ZnO, with crystallite sizes mostly in the range of 20-50 nm. The lab worksheet is graded on a 10-point scale, and class averages have ranged from 8.4-9.0 out of 10. Students usually correctly interpret their results to determine whether or not they have successfully made ZnO. Some students make unit conversion errors in calculating crystallite sizes. Students sometimes get confused between d-spacings and particle sizes and incorrectly say that a structure with a larger unit cell would be expected to have narrower diffraction peaks.

Description: 

I designed this lab experiment to introduce students to the uses of powder X-ray diffraction in the context of the synthesis of a technologically relevant material. Zinc oxide nanoparticles can be synthesized readily with reagents that are inexpensive and relatively benign with regard to student use and waste disposal. Two experiments described in J. Chem. Ed. feature synthesis of ZnO nanoparticle sols and films and their characterization by UV-vis spectroscopy (see web resources below). This new experiment shows powder X-ray diffraction as a tool for characterization of nanomaterials. 

In the experiment, students use the base hydrolysis of zinc acetate in ethanol to prepare a sol of ZnO particles. Students add water to the sol to agglomerate the particles and use centrifugation and drying to isolate a solid for characterization by powder X-ray diffraction. Students identify the phase of their solids by matching to a reference from the Powder Diffraction File, and then estimate crystallite sizes by applying the Debye-Scherrer equation. 

This material is based in part upon work supported by the National Science Foundation under grant number DMR-0922588. Any opinions, findings, and conclusions or recommendations are those of the author and do not necessarily reflect the views of the National Science Foundation.

Prerequisites: 
Corequisites: 
Course Level: 
Learning Goals: 

Students should be able to:

1) Explain how solution reaction conditions can be designed to control particle growth
2) Use powder diffraction data to identify phases and approximate crystallite sizes in a sample
3) Apply Bragg’s law to predict how diffraction peak positions compare for isostructural compounds with different unit cell dimensions
4) Explain why X-rays are dangerous and what safety features are built into a modern X-ray diffractometer

Equipment needs: 

Reagents
Absolute ethanol
Deionized water
Zn(OAc)2·2H2O (0.55 g per reaction)
LiOH·H2O (0.15 g per reaction)
Note: When exposed to humidity and CO2 over time, lithium hydroxide can convert to lithium carbonate. When partially converted material is used in the reaction, students have difficultly fully dissolving the lithium salt in ethanol, and the yield is reduced significantly. Storing the LiOH well sealed and away from humidity (for example, in a desiccator) preserves the salt.

 

Equipment (for each student or partnership):
Weighing paper or boats
Metal spatulas
two magnetic stirplates
two magnetic stirbars
two 125-mL Erlenmeyer flasks
two basins for ice baths – at least one will need to be placed on the stirplate and should be of a non-ferromagnetic material
watch glass
centrifuge
three 13 x 100 mm test tubes
Pasteur pipets
Rubber bands
Permanent marker

 

Equipment (for the entire class):
Balances
UV light
Abderhalden drying pistol or other apparatus for drying under vacuum
Oven (can be a drying oven) capable of holding a temperature of 120 oC
Access to a powder X-ray diffractometer

Implementation Notes: 

Students typically work in partnerships for the experiment. I do the experiment over two weeks. Students work full-time on the synthesis during the first week and do the characterization by powder X-ray diffraction in the second week. Because of radiation safety regulations, the students can't run the diffractometer themselves without completing safety training that is prohibitively time-consuming for the number of students involved. The diffractometer is run by a fully trained undergraduate TA or by me, and the students prepare their samples for the experiment, see the instrument working, and process their data files on the computer.

 

Each partnership spends approximately 15 minutes at the instrument for the characterization, so there is time during the second week for another activity. A good complementary activity that students can easily step in and out of is solid-state model building. I do this lab during the solid-state structures unit in my intermediate-level inorganic course. In the lecture part of the course, students are introduced to X-ray diffraction, with a focus on the Bragg law and the relationship between structures and diffraction peak positions.

Time Required: 
one three-hour lab session and 15-20 minutes per partnership during a second lab period
25 May 2011

Catalysis using functionalized mesoporous silica

Submitted by Randall Hicks, Wheaton College
Evaluation Methods: 
Unless a student has done some independent research (lab or literature) in this area previously, I expect that none of them will have any experience with this work. Therefore, I assess on the effort that students made to answer the assigned questions and on their contribution to in-class discussion. The instructor of record (for senior seminar) is also present to observe the class proceedings and can decide how to integrate that into an overall grade for the course. 
Evaluation Results: 

Without the review of unfamiliar terms and concepts on the first day of the two-day activity, I doubt that many students would be able to tackle this paper. However, after going through all that, students do a fair job of answering the questions.

The answers to most of the "general questions" can be found from web searching. The students that are motivated to do so have dug up answers for these questions. Question #6 is difficult for them, but serves as a good point to initiate conversation about why larger mesoporous materials are useful. Question #7 is also foreign, but it usually comes up in the first class and so students can piece together a response for it here. 

Answering the "characterization method" questions has proven more difficult for the students, particulalry because most if not all of them lack experience with x-ray diffraction and gas adsorption techniques. They can look up Bragg's Law and calculate a parameter given the other values (solve for x, essentially) even if they don't know exactly what that value represents. A4 is particularly difficult as they need to find the answer in the accompanying paper. Responses to questions on gas adsorption are understandably murkier yet. Again, this is where I can go into more detail on the method in class discussion. On the other hand, questions in C and D on UV-Vis and IR, respectively, are easier for them given their familiarity with those techniques. These questions are usually answered well. D1, on site-isolation, sometimes requires further explanation. And, finally, while students have NMR experience from organic, they're not usually knowledgeable on solid-state NMR. Some of these answers can be found online or in the paper, but this is another are where a short discussion is helpful.

Depending on the length of discussion in a particular class, there is not always time to fully get into the catalysis results. However, the answers to these questions can be found in the main manuscript and are correctly reported.   

Description: 

This paper, while not fundamentally groundbreaking, serves as a nice introduction to the field of mesoporous materials. I like that it covers synthesis, characterization, and an application of the materials. I have used this paper in our senior seminar course as the basis for discussion of this area of chemistry. Discussion questions cover aspects of sol-gel chemistry, powder diffraction, gas adsorption, IR, solid state NMR, UV-Vis, and catalysis.  

Prerequisites: 
Course Level: 
Learning Goals: 

Upon reading this paper, students should be able to:

• Describe at least one method by which mesoporous materials can be both synthesized and functionalized

• Explain how x-ray diffraction, gas adsorption, solid state NMR (and to a lesser extent, IR and UV-Vis) can be used to characterize mesoporous materials

Implementation Notes: 

As part of our seminar, each faculty member rotates through to present a paper for discussion in his or her area of chemistry. The class meets for 1 hr 20 minutes twice a week (Tuesday and Thursday). Students are given the paper on a Tuesday, without much preface, and are asked to briefly read over the work for Thursday. In class on that Thursday, I have them to present an overview of the paper and submit any terms with which they are unfamiliar. I spend the majority of that day giving an introduction to the field, defining unfamilair terms, and answering questions. Then I distribute a handout with specific questions for the students to answer. Some questions are to be done by all, others are assigned in groups. While the groups are evenly populated, I often assign a different number of question to each group. For instance, because students have been introduced to IR, NMR, and UV-Vis, I have one group tackle all three of these sections on the assignment. For topics with which they're not likely familiat (XRD, gas adsorption), I assign one of these per group. They have until the following Tuesday to work on the questions. At that point, I ask students to present their answers, and we resume the class discussion. (I have attached the handout that I give to students, and a version with my answers, below.) 

Related note: Although we are moving to a two-course inorganic sequence in AY 2012-13, I do not have the ability to "squeeze" materials chemistry into my (currently) one semester course; I therefore relish the opportunity to present this paper in our seminar course. If you have the time to cover materials in your normal inorganic sequence, you may be able to present this paper in one class instead of two. 

If you have faculty privileges on VIPEr, then solutions to the questions can be found in the linked learning object (see related activities).

Time Required: 
Two (2) 80-min classes
23 Aug 2010

Using Solid State Chemistry and Crystal Field Theory to Design a New Blue Solid

Submitted by Barbara Reisner, James Madison University
Evaluation Methods: 

When the literature discussion was used at Reed in Spring 2011, the discussion questions were collected and graded on a 10 point scale, 1 point for each question with the exception of #5, worth 2 points, plus an additional point for effort.

Evaluation Results: 

Of the 17 students that turned in discussion questions, 2 students (12%) earned 9.5 points out of 10, 7 students (41%) earned 8-9 points, 4 students (24%) earned 7-8 points, and 4 students (24%) earned 6-7 points.

On question 1 (ionic radii), most students did not cite the source of their data or did not specify a coordination number for the ions, and fractions of a point were deducted for these omissions.  On question 2 (bond distances), 7 of 17 (41%) students did not calculate predicted bond distances from the ionic radii.  In general, students did very well on questions 3 and 4.  Question 5 proved more of a challenge.  Common errors included no drawings of the d-orbitals in the trigonal prismatic crystal field or unsatisfactory explanations for the crystal field splitting pattern.  Only 5 of 17 students (29%) provided the correct answer of magnetism on question 6.  Other answers were incomplete or did not explain how the experiment would verify the presence of high-spin Mn3+.  On question 7, nearly all students successfully converted the energy scale to photon wavelengths, but 4 students mislabeled the electromagnetic region, as either all infrared or all ultraviolet.  Six of 17 students (35%) answered question 8 correctly.  The most common error was no explicit indication that transitions in the octahedral geometry are symmetry forbidden by the LaPorte selection rule, whereas this rule is relaxed in trigonal bipyramidal coordination.

Description: 

This communication from the Journal of the American Chemical Society (J. Am. Chem. Soc. 2009, 131, 17084-17086.  doi:10.1021/ja9080666) describes the use of classic solid state chemistry to dope Mn3+ in two different host oxide structures to create new blue pigments.  The key to the blue color is the unusual trigonal bipyramidal coordination of the Mn3+ ion in these structures.  Discussion of this paper in class provides an opportunity to discuss solid solution chemistry in extended structures, including both their synthesis and characterization as well as illustrate the application of crystal field theory to understand the color of a transition metal doped oxide.  An extensive list of discussion questions is provided so that the learning activity can be tailored to a variety of different curricular uses and student backgrounds.

Prerequisites: 
Corequisites: 
Learning Goals: 

After reading and discussing this paper, a student will be able to:

  • Describe the basic considerations in the design, synthesis, and characterization of solid solutions in extended structures.
  • Identify and describe the distinguishing features of several different mixed metal oxide structures.
  • Given structural information, apply the principles of crystal field theory to explain the color and electronic spectroscopy of a transition metal ion doped oxide.
Implementation Notes: 

An extensive list of potential discussion questions was developed by Barbara Reisner and Maggie Geselbracht, two faculty trained as solid state chemists so that other faculty would have a range to choose from and use, depending on their curricular goals.  We believe that this is an ideal paper to introduce extended solids into the inorganic curriculum with the “hook” for both faculty and students of an easy connection to coordination chemistry.
 
The first time this learning object was used in the classroom was by Barb at James Madison University in Fall 2009 in a second semester Inorganic Chemistry Course. This paper was not originally used as a literature discussion but instead turned into a lecture. The lecture was used to tie up a unit on solid state chemistry, and the figures in the paper to discuss solid state structures and ionic radii; basic crystallography, powder diffraction, and Vegard’s Law; and crystal field theory.

Maggie used this literature discussion activity as the final conference for her sophomore-level inorganic chemistry course at Reed College in Spring 2011. She selected 8 of the discussion questions from the full list and provided them to her students in advance of the conference meeting. This shortened list is available as an attachment above. Students were asked to read the paper and write out the answers to the discussion questions prior to the discussion. The solutions document to these 8 questions is available to registered faculty users on VIPEr.

 

Time Required: 
50 minutes
28 Jun 2010

Powder Diffraction Crystallography Instructional Materials

Submitted by Barbara Reisner, James Madison University
Description: 
Brian Toby (Argonne National Labs) has assebled an excellent series of tutorials on using the Rietveld analysis technique for powder diffraction data. Tutorials range from an "Introduction to Crystallography" and "Getting Started with Rietveld" to using the "Le Bail Intensity Extraction" Method to "Advanced Rietveld Techniques."
Course Level: 
13 Aug 2009

IUCr Teaching Resources

Submitted by Barbara Reisner, James Madison University
Description: 
Course Level: 
Topics Covered: 
Prerequisites: 
Corequisites: 
18 Jun 2009

Crystallography (in English) & Evaluating Crystal Structures

Submitted by Barbara Reisner, James Madison University
Description: 

The University of Oklahoma has put together a nice website on Crystallography which includes a standard introduction to crystallography & crystal symmetry. I also like some of the features that you don't normally come across including evaluating crystal structures and twinning.

Topics Covered: 
Prerequisites: 
Course Level: 
Corequisites: 
Implementation Notes: 

I intend to share this with any students reading papers which involve crystal structures. It might be a useful reference for teaching crystallography in a course that isn't entirely devoted to crystallography.

16 Jun 2009
Evaluation Methods: 
Adam Johnson from Harvey Mudd College and I collaborated to develop several peer evaluation rubrics for this learning object.  A peer evaluation form was handed out to the “audience” that included a copy of the discussion questions assigned to the presenting team.  The students in the audience were asked to answer the questions based on what they learned from the presenting team as well as evaluate the presenters both individually and as a team in their effectiveness.  An intragroup peer evaluation was handed out to the presenting team in which the team members were asked to numerically rate themselves (on a scale of 1 to 10) and the other members on content, reliability, preparation, and style.
Evaluation Results: 
The PowerPoint presentations were generally quite effective, although most students agreed that this format did not work very well to stimulate discussion.  Both teams were focused on getting through the presentations.  While they would answer my questions, there were not a lot of questions from the other students.  However, content was effectively conveyed as measured by the observation that nearly all audience members were able to answer the questions based on the presentations.  In the intragroup evaluations, some students were particularly hard on themselves.  I ended up averaging their scores, and adding in my own score to reach a final assessment for this project.
Description: 
This literature discussion activity is one of a series of “Energy Nuggets,” small curricular units designed to illustrate: The Role of Inorganic Chemistry in the Global Challenge for Clean Energy Production, Storage, and Use.

The chemistry of nitrogen fixation, converting N2 into NH3, serves as the gateway into the nitrogen cycle and requires a catalyst.  Industrially, this process is carried out at high temperatures and pressures and consumes a large amount of energy.  Inorganic chemists have long been interested in how nature accomplishes this same reaction under ambient conditions with the enzyme nitrogenase.  This learning object examines two key papers related to this field through a series of discussion questions.  In the first paper by Doug Rees’s group, a high resolution X-ray crystal structure reveals the details of the active site of nitrogenase.  The second paper from Richard Schrock’s group reports a synthetic molybdenum complex that catalytically converts N2 into NH3.  

Corequisites: 
Prerequisites: 
Course Level: 
Learning Goals: 

After reading these papers and working through the discussion questions, a student will be able to:

  • Discuss the industrial production of ammonia including the chemistry, the production scale, and the energy requirements.
  • Describe our current level of understanding of the enzyme nitrogenase and the structure of the active site of dinitrogen reduction in the Fe-Mo cofactor.
  • Discuss the structure and characterization of the first dinitrogen complex as well as later complexes capable of reducing N2 to NH3 at a metal center.
  • Describe the unique characteristics of the Schrock catalyst, present the proposed mechanism for the reduction of N2 to NH3, and the clever conditions used to achieve catalytic turnover.
  • Use Web of Science to conduct a citation search and discuss the impact of a landmark paper on related research.
  • Gain confidence and experience in oral presentation skills including the use of PowerPoint.
Implementation Notes: 
I divided my class into two teams, one team assigned to each of the two papers.  I let the students choose which team they were on and sign up for a discussion question based on their interest.  The team was responsible for teaching the rest of us what the paper was all about during a class meeting (80 minutes).  The students used PowerPoint to present the answers to the discussion questions in some unified fashion.  The assumption was that the other team had not read the paper that was being presented, but they were asked to record their answers to the discussion questions based on what they learned in class.
Time Required: 
2 class sessions
4 Jun 2009

Energy Nuggets: MOF’s for CO2 Sequestration

Submitted by Maggie Geselbracht, Reed College
Evaluation Methods: 
Students’ participation in the in-class discussion, the online class forum, and their level of effort finding the answers to the discussion questions prior to class all contribute to their evaluation for this assignment.
Evaluation Results: 
The in-class and online discussion of this paper was quite lively.  Students had a lot of questions on how surface area was measured and we looked at a number of different MOF structures to gain a sense of how vast the field was.  Students were fairly skeptical of whether or not this work satisfied the significance of a JACS communication, particularly because they did not believe these materials could be practically applied in the manner suggested by the authors.  This led to an active discussion of academic research vs. commercialization of a product, and the recent C&E News article on commercialization of MOF’s (see link above) was a perfect fit.  Most of the students did not buy the use of CO2 sequestration materials and thought that this area of research should be fairly low on the list of research funding priorities.
Description: 
This literature discussion activity is one of a series of “Energy Nuggets,” small curricular units designed to illustrate: The Role of Inorganic Chemistry in the Global Challenge for Clean Energy Production, Storage, and Use.

This communication is a nice introduction to the field of metal organic frameworks (MOF’s) and the characterization and potential applications of porous materials.  Rather than tackling hydrogen or methane storage, materials for carbon dioxide sequestration is an often-overlooked area that offers many opportunities to discuss the same chemistry.  And while many students want to focus only on renewable energy, realizing that we will not stop burning coal anytime in the near future is an important piece of the energy challenge.  From here, one could easily continue on in the rich field of MOF’s in numerous directions.
Course Level: 
Learning Goals: 
After reading and discussing this paper, a student will be able to:
• Describe the general structural features, properties, and potential applications of a MOF (metal-organic framework)
• Distinguish between the terms physisorb and chemisorb and describe in qualitative terms how the surface areas of porous materials are characterized
• List the important factors in designing materials for hydrogen storage and/or carbon dioxide sequestration
• Understand the significance of a JACS communication including the criteria for publication
• Engage in a discussion relating a very specific area of academic research to the larger needs and challenges facing the global community
Implementation Notes: 
Out of a class of 14 students, I divided up and assigned the discussion questions so that each question was answered by 4-5 students and each student had 2-3 questions to prepare in addition to the ones assigned to everyone.  I also asked the students to begin discussing the paper online in the course Moodle forum before we met for class.
Time Required: 
1 hour discussion
13 Apr 2009
Description: 

The Interdisciplinary Education Group at the University of Wisconsin Madison Materials Research Science and Engineering Center (MRSEC) has a fabulous website with a wide variety of great resources for teaching about materials and the nanoworld at all levels.  A favorite "corner" of this website that I refer to a lot in my own teaching is the library of so-called Resource Slides on a variety of topics.  These Resource Slides are divided up into 36 topical Slide Shows and include wonderful graphics to use in class presentations.   Slide Shows include:

  • Amorphous Metal
  • Defects
  • DNA Barcode Methods
  • Electrorheology
  • LED applications
  • Metals
  • Nanowire Sensors
  • oLED
  • Piezoelectricity
  • Scanning Microscopies
  • Societal Implications
  • Structure and Properties
  • CD & DVD
  • Diffraction
  • Electronic Structure
  • Ferrofluid
  • Liquid Crystals
  • The Nanoscale
  • Nickel Nanowire Synthesis
  • Periodic Properties and LEDs
  • p-n junctions
  • Semiconductor
  • Solar Power
  • Thermoelectric Devices
  • Computer Technology
  • DNA
  • Electrons and magnetism
  • Gold
  • Lithography
  • Nanotubes
  • NiTi Memory Metal
  • Photonics
  • Quantum Dots
  • Semiconductor Sensors
  • Spectroscopy
  • Unit Cells and Stoichiometry
Prerequisites: 
Corequisites: 
Learning Goals: 

Implementation Notes: 
I use the graphics in many of these Slide Shows during class to illustrate the applications of many materials in working devices or more often to supplement the textbook I am using with more in-depth information on the structure and bonding in metals and semiconductors.  Some of these slide shows are aimed at a very general audience and so could be used in a general chemistry course.  But in other cases, I think they are more appropriate for an inorganic chemistry course in which the electronic structure of solids follows naturally from an in-depth discussion of molecular orbitals.
12 Jan 2009

House: Inorganic Chemistry

Submitted by Adam R. Johnson, Harvey Mudd College
Description: 

House (Inorganic chemistry):  The book is divided into 5 parts:  first, an introductory section on atomic structure, symmetry, and bonding; second, ionic bonding and solids; third, acids, bases and nonaqueous solvents; fourth, descriptive chemistry; and fifth, coordination chemistry.  The first three sections are short, 2-4 chapters each, while the descriptive section (five chapters) and coordination chemistry section (seven chapters covering ligand field theory, spectroscopy, synthesis and reaction chemistry, organometallics, and bioinorganic chemistry.) are longer.  Each chapter includes references (both texts and primary literature) for further reading, and a few problems (answers not available in the back of the book). 

I thought the text was generally good.  This text felt aimed at the introductory one-semester inorganic course offered at most schools rather than an advanced (senior/grad) course.  Although MO theory is developed in the text, most of the coordination chemistry is described using crystal field theory, though a short section on MO theory for complexes is included.  The sections on descriptive chemistry of the elements are very good and not overloaded with too much information, and the writing style (throughout the text) is easy to read and conversational.

My main complaint about the book, and this may seem petty, is that the molecular orbitals (throughout) do not accurately depict the way actual orbitals look;  they are too "pointy." 

The list price for the student text is $99.95 for a paperback, 864p version.

Prerequisites: 
Corequisites: 
Course Level: 

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